Imaging device

ABSTRACT

An imaging device having a pixel including a photoelectric converter that converts incident light into charges, and a reset transistor having a first source, a first drain and a first gate, one of the first source and the first drain coupled to the photoelectric converter. The imaging device further including first voltage generating circuity that generates a first voltage; second voltage generating circuity that generates a second voltage, the second voltage generating circuity being different from the first voltage generating circuity; and first switching circuity that causes either the first voltage generating circuity or the second voltage generating circuity to selectively couple to the other of the first source and the first drain of the reset transistor.

CROSS-REFERENCE OF RELATED APPLICATIONS

This application is a Continuation application of U.S. patentapplication Ser. No. 15/190,368, filed on Jun. 23, 2016, which in turnclaims the benefit of Japanese Application No. 2015-136328, filed onJul. 7, 2015 and Japanese Patent Application No. 2016-055777, filed onMar. 18, 2016, the entire disclosures of which Applications areincorporated by reference herein.

BACKGROUND 1. Technical Field

The present disclosure relates to an imaging device (also called an“image sensor”).

2. Description of the Related Art

In recent years, video cameras and digital cameras have been inwidespread use. Such cameras include a charge coupled device (CCD) imagesensor or a complementary metal oxide semiconductor (CMOS) image sensor.In particular, CMOS image sensors are becoming more mainstream. One ofthe reasons is that since a peripheral circuit can be integrated into asingle chip, a signal can be read out of the imaging device at highspeed and, thus, the imaging device can be improved in terms of theirspeed and resolution.

For example, Japanese Unexamined Patent Application Publication No.2011-228621 describes an imaging device using an organic photoelectricconversion film in a light receiving unit thereof. In addition, JapaneseUnexamined Patent Application Publication No. 2011-109282 describes animaging device including a sample-and-hold circuit.

SUMMARY

An imaging device capable of further reducing horizontal line noise isexpected to be developed. One non-limiting and exemplary embodimentprovides an imaging device capable of reducing horizontal line noisewhile maintaining a high frame rate.

In one general aspect, the techniques disclosed here feature an imagingdevice having a pixel comprising a photoelectric converter that convertsincident light into charges, and a reset transistor having a firstsource, a first drain and a first gate, one of the first source and thefirst drain coupled to the photoelectric converter. The imaging devicefurther comprising first voltage generating circuity that generates afirst voltage; second voltage generating circuity that generates asecond voltage, the second voltage generating circuity being differentfrom the first voltage generating circuity; and first switching circuitythat causes either the first voltage generating circuity or the secondvoltage generating circuity to selectively couple to the other of thefirst source and the first drain of the reset transistor. It should benoted that general or specific embodiments may be implemented as asystem, a method, an integrated circuit, a computer program, a storagemedium, or any selective combination thereof.

According to the aspect of the disclosure, an imaging device capable ofreducing horizontal line noise while maintaining a high frame rate canbe provided.

Additional benefits and advantages of the disclosed embodiments willbecome apparent from the specification and drawings. The benefits and/oradvantages may be individually obtained by the various embodiments andfeatures of the specification and drawings, which need not all beprovided in order to obtain one or more of such benefits and/oradvantages.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a timing diagram of a typical operation performed by anorganic CMOS image sensor including a 3Tr readout circuit;

FIG. 2 illustrates a random horizontal line noise generating mechanism;

FIG. 3 is a schematic illustration of the circuit configuration of animaging device according to a first exemplary embodiment;

FIG. 4A is a schematic illustration of an exemplary circuitconfiguration of a reset voltage generating circuit;

FIG. 4B is a schematic illustration of an example of the configurationof a reset voltage generating circuit including a single voltage controlunit;

FIG. 5 is a timing diagram illustrating the drive timing of the imagingdevice according to the first exemplary embodiment;

FIG. 6 is a timing diagram illustrating another drive timing of theimaging device according to the first exemplary embodiment;

FIG. 7 is a schematic illustration of the circuit configuration of animaging device according to a second exemplary embodiment;

FIG. 8A is a schematic illustration of a typical example of the circuitconfiguration of a reference voltage applying circuit included in theimaging device.

FIG. 8B is a schematic illustration of an example of a reference voltageapplying circuit including a single voltage control unit;

FIG. 9 is a timing diagram of the drive timing of the imaging deviceaccording to the second exemplary embodiment;

FIG. 10 is a timing diagram illustrating the enabled period of each of afirst reference voltage applying circuit and a second reference voltageapplying circuit in consecutive frame scanning period;

FIG. 11 is a timing diagram of another example of the timing of controlof the switches in a second switching circuit;

FIG. 12 is a timing diagram illustrating an example of the timing ofcontrol of the switches in the reference voltage applying circuit inconsecutive frame scanning period;

FIG. 13A is a schematic illustration of the circuit configuration of animaging device according to a third exemplary embodiment;

FIG. 13B is a schematic illustration of an example of the circuitconfiguration of a bias circuit including a single voltage control unit;

FIG. 14 is a schematic illustration of the circuit configuration of animaging device according to a fourth exemplary embodiment;

FIG. 15 is a schematic illustration of an example of the timing ofcontrol of the switches in the second switching circuit of the imagingdevice;

FIG. 16 is a timing diagram illustrating another example of the timingof control of the switches in the second switching circuit;

FIG. 17 is a schematic illustration of the circuit configuration of animaging device according to a fifth exemplary embodiment;

FIG. 18 is a schematic illustration of an exemplary circuitconfiguration of a pixel capable of forming a feedback path;

FIG. 19 is a schematic illustration of another exemplary circuitconfiguration of a pixel capable of forming a feedback path;

FIG. 20A is a schematic illustration of the circuit configuration of animaging device according to a sixth exemplary embodiment;

FIG. 20B is a schematic illustration of another example of the circuitconfiguration of the imaging device according to the sixth exemplaryembodiment; and

FIG. 21 illustrates a modification of the circuit configurationaccording to the sixth exemplary embodiment.

DETAILED DESCRIPTION

Before exemplary embodiments of the present disclosure are described,the issues that the present inventers have found in existing imagingdevices are described.

In recent years, the area per pixel of an imaging device has decreasedwith increasing number of pixels used in the imaging device.Accordingly, a decrease in the sensitivity of a pixel and a decrease inthe number of saturation electrons are recognized as major problems. Tosolve the problems, an organic CMOS image sensor that uses an organicphotoelectric conversion film in a light receiving unit has beendeveloped.

For example, the organic CMOS image sensor described in JapaneseUnexamined Patent Application Publication No. 2011-228621 has an organicphotoelectric conversion film disposed above a readout circuit. Thereadout circuit is electrically connected to the light receiving unitincluding the organic photoelectric conversion film via a metal wiringline. The organic CMOS image sensor can maintain the area of the lightreceiving unit even when the pixel size is reduced. Thus, thesensitivity of a pixel and the number of saturation electrons can bemaintained at a high level.

In general, CMOS image sensors (including an organic CMOS image sensor)include a readout circuit including three transistors (hereinafterreferred to as a “3Tr readout circuit”) or a readout circuit includingfour transistors (hereinafter referred to as a “4Tr readout circuit”).Each of the types of readout circuit is described in detail below.

The organic CMOS image sensor described in Japanese Unexamined PatentApplication Publication No. 2011-228621 includes a 3Tr readout circuit.In the readout circuit, a light receiving unit is electrically connectedto a floating diffusion (FD) node. In addition, the readout circuitincludes a reset transistor that resets the charge accumulated in the FDnode. Hereinafter, resetting of the charge accumulated in the FD node isreferred to as “resetting of a pixel”.

FIG. 1 illustrates a typical timing of the operation of an organic CMOSimage sensor including a 3Tr readout circuit. For simplicity ofdescription, the number of pixels arranged in the vertical direction istwo. Hereinafter, the first row is discussed. The pixel is reset at atime t1 first. As used herein, resetting of all the pixels in a certainrow is referred to as “row reset”. In an example illustrated in FIG. 1,a period required for row reset of the first row is the period from thetime t1 to a time t2. This period is referred to as “row reset period”.Through row reset, the charge in the FD nodes in the pixels arranged ina row which is a target of row reset is discharged. Note that the rowreset performed for each of the rows at the beginning of one frameperiod is generally referred to as an “electronic shutter (inparticular, rolling shutter) operation”. By controlling the period ofthe electronic shutter operation, that is, by controlling the row resettiming, the exposure period can be controlled.

The exposure period is the period from the time t2 to a time t3. Theexposure starts at the time t2, and a signal level in accordance withthe charge generated through the exposure is read out at the time t3(first signal readout). Thereafter, row reset is performed again, and adark signal level obtained when no charge is generated in the FD is readout (second signal readout). The signal level serves as a referencelevel used when a pixel signal is obtained from a pixel. That is, thedifference between the signal level obtained in the first signal readoutand the signal level obtained in the second signal readout is acquired.Thereafter, row reset is performed for the next frame at a time t4.Subsequently, a similar operation is repeated. In addition, for each ofthe other rows, row reset and signal readout are sequentially performedin the same manner as for the first row. As used herein, the time periodfrom the time t3 to the time t4 is referred to as a “signal readoutperiod”.

In the present specification, a period according to one frame for onerow is referred to as “one frame period”. In the above example, oneframe period may correspond to a period from the start of the row resetperiod to the end of the signal readout period. That is, one frameperiod may correspond to a period from time t1 to time t4 in FIG. 1.And, a period according to one frame for all the rows is referred to as“one frame scanning period”. In the above example, one frame scanningperiod may correspond to a period from the start of the row reset periodof the first row to the end of the signal readout period of the lastrow. Note that in FIG. 1, setting is made so that the exposure period isthe longest, and the row reset serving as an electronic shutter isperformed immediately after the signal readout period for the previousframe, for each row. At that time, as described above, by delaying thetime point for the row reset, the length of the exposure period can bedecreased.

In 3Tr readout circuits, a transfer operation of charge from the lightreceiving unit to the FD is not performed. Accordingly, even when thelight receiving unit is not fully depleted, transfer noise and aresidual image are negligibly generated. In contrast, 4Tr readoutcircuits include a transfer transistor for transferring all the signalcharge from the light receiving unit to the FD (this operation isreferred to as “complete transfer”). In 4Tr readout circuits, ifcomplete transfer fails, incomplete transfer noise and a residual imageare generated. Accordingly, full depletion of the light receiving unitis required.

In organic CMOS image sensors, it is difficult to perform completetransfer because of their structures. If the structure of an organicCMOS image sensor is taken into account, a 3Tr readout circuit can bemore easily applied to the sensor than a 4Tr readout circuit. However,in 3Tr readout circuits, a reset voltage applied to a plurality ofpixels commonly connected in the column direction and a bias voltageapplied to a bias circuit serving as a current source for reading outthe voltage signals of a pixel are likely to vary row by row during theexposure period. The variations generate horizontal line noise atrandom. As used herein, such noise is referred to as “random horizontalline noise”. In particular, in a moving image, the random horizontalline noise randomly and repeatedly appears. Thus, the random horizontalline noise is one of the factors that decrease the quality of the image.

The mechanism of generation of random horizontal line noise is describedbelow with reference to FIG. 2. FIG. 2 illustrates the random horizontalline noise generating mechanism, that is, FIG. 2 is a schematicillustration of a variation of the reset voltage during each of the rowreset period, the exposure period, and the signal readout period. Thereset voltage serves as a reference voltage used to reset the FD of apixel to the reference level. The reference voltage can be provided fromthe outside or can be generated inside. When the reference voltage isprovided from the outside, the reference voltage is influenced by thedisturbance noise received from the power supply and a set board. Incontrast, when the reference voltage is generated inside, the referencevoltage is influenced by the thermal noise and the 1/f noise receivedfrom a transistor in a voltage generation circuit. Note that the randomhorizontal line noise caused by a variation of the reset voltage isgenerated in a 3Tr readout circuit and is not generated in a 4Tr readoutcircuit. The reason is described below.

In 4Tr readout circuits, a transfer transistor is connected between thephotoelectric conversion unit and the FD. In such a readout circuit, theFD is reset, and a signal of a reference level is read out first.Thereafter, the transfer transistor is turned on, and the accumulatedcharge is transferred from the photoelectric conversion unit to the FD.Subsequently, the signal is read out. The difference between the readoutsignal and the reference signal is obtained as a pixel signal. Asdescribed above, since a reset operation is not performed between thetwo signal readout operations, random horizontal line noise caused by avariation of the reset voltage is not generated.

In contrast, in 3Tr readout circuits, the photoelectric conversion unitis not electrically insulated from the FD. As described above, two rowreset operations, that is, the row reset serving as an electronicshutter to set the FD to the reference level and the row reset duringthe signal readout period are performed for each of the rows in oneframe period. If the reset voltages in the two row reset operations varydue to the influence of the above-described noise and, thus, differ fromeach other, a signal offset that temporally varies row by row is addedto the pixel signal. The signal offset is detectable by the eyes in theform of random horizontal line noise.

The random horizontal line noise may also be generated due to avariation of the voltage of a bias line of a current source used forreading out a voltage signal of a pixel into a vertical signal line anda variation of the voltage of a lamp voltage line used foranalog-to-digital (AD) conversion. To prevent the random horizontal linenoise generated by these voltage variations, a technique using asample-and-hold circuit during a period from resetting of the FD tocompletion of the AD conversion is widely used. For example, the 4Trreadout circuit described in Japanese Unexamined Patent ApplicationPublication No. 2011-109282 employs such a technique.

Even in 3Tr readout circuits, a sample-and-hold circuit can hold thereset voltage during a period from a time t1 to a time t4 (refer to FIG.1). However, in recent years, the frame rate has been increased.Accordingly, in some cases, an image sensor is driven so that signalreadout scanning during one frame period and the shutter scanning forthe next frame are performed at the same time. That is, in some cases,an image sensor is driven so that a frame scanning period for one framepartially overlaps a frame scanning period for the next frame. Toprevent the occurrence of random horizontal line noise, it is desirablethat the reset voltage be held throughout one frame scanning period.However, according to the drive technique in which signal readoutscanning and the shutter scanning according to the frames contiguouswith each other are performed in an overlap period, the reset voltageholding period extends across two frames. As described above, it isdifficult to increase the frame rate and reduce noise caused by asample-and-hold operation at the same time.

As illustrated in FIG. 2, if the reset voltage is not sampled and held,the reset voltage varies at every moments. In this example, theinstantaneous value of the bias voltage during the signal readout periodvaries by up to ΔV1 when the average of the bias voltages over the rowreset period serving as an electronic shutter is used as a referencevalue. According to the existing technology described in JapaneseUnexamined Patent Application Publication No. 2011-109282, thesample-and-hold circuit holds the reset voltage during a period from thecompletion of signal readout of the accumulated charge throughcompletion of signal readout of the reference level and samples a signalduring the other period. By performing such an operation, a variation ofthe reset voltage during the signal readout period (a time period fromthe time t3 to the time t4 in FIG. 1) can be prevented.

However, if a 3Tr readout circuit is used, it is difficult to prevent avariation of the reset voltage caused by noise generated during theexposure period (a period from the time t2 to the time t3 in FIG. 1) byusing such an operation. In an example illustrated in FIG. 2, theaverage of the reset voltages during the signal readout period varies byΔV2 on the basis of the average of the bias voltages during the rowreset period serving as the electronic shutter (see a graph in themiddle). As described above, if the reset voltage varies during oneframe period, it is difficult for an existing technique to effectivelyprevent the random horizontal line noise.

As a result of the study of such problems, the present inventorsconceived the idea of an imaging device having a novel configurationthat addresses the above-described tradeoff.

The present disclosure provides imaging devices having theconfigurations described below.

Configuration 1

An imaging device includes

a plurality of pixels arranged two-dimensionally,

a row scanning circuit that generates a row scanning signal,

a plurality of reset voltage lines each disposed for one of rows andconnected to the pixels in the row,

first and second reset voltage generating circuits capable of beingelectrically connected to the pixels via the reset voltage lines, whereeach of the first and second reset voltage generating circuits generatesa reset voltage, and

a first switching circuit that electrically connects one of the firstand second reset voltage generating circuits to the pixels for an oddnumbered frame and electrically connects the other of the first andsecond reset voltage generating circuits to the pixels for an evennumbered frame.

The imaging device having Configuration 1 can prevent a variation of thereset voltage caused by, for example, disturbance noise or thermalnoise.

Configuration 2

An imaging device includes

a plurality of pixels arranged two-dimensionally,

a row scanning circuit that generates a row scanning signal,

a plurality of column signal lines each disposed for one of columns andconnected to the pixels in the column,

a plurality of inverting amplifiers each disposed for one of the columnsand connected to the column signal line for the column,

a plurality of feedback signal lines each disposed for one of thecolumns and connected to an output terminal of the inverting amplifierfor the column,

first and second reference voltage applying circuits capable of beingelectrically connected to a reference voltage input terminal of each ofthe inverting amplifiers via a common reference voltage line, where eachof the first and second reference voltage applying circuits generates areference voltage for the inverting amplifiers, and

a second switching circuit that electrically connects one of the firstand second reference voltage applying circuits to the reference voltageinput terminals of the inverting amplifiers for an odd numbered frameand electrically connects the other of the first and second referencevoltage applying circuits to the reference voltage input terminals ofthe inverting amplifiers for an even numbered frame.

The imaging device having Configuration 2 can prevent a variation of thereference voltage caused by, for example, disturbance noise or thermalnoise.

Configuration 3

The imaging device of the configuration 2 further includes

first and second bias circuits disposed for each of the columns andcapable of being electrically connected to a plurality of load unitsconnected to the column signal line for the column, where each of thefirst and second bias circuits generates a control voltage that controlsthe load units, and

a third switching circuit that electrically connects one of the firstand second bias circuits to the load units for an odd numbered frame andelectrically connects the other of the first and second bias circuits tothe load units for an even numbered frame.

The imaging device having Configuration 3 can prevent a variation of thebias voltage caused by, for example, disturbance noise or thermal noise.

Configuration 4

In the imaging device of any one of the configurations 1 to 3, each ofthe pixels includes

a photoelectric conversion unit that photoelectrically converts incidentlight and

a signal detection circuit including a reset circuit and an amplifiercircuit, and the signal detection circuit detects a signal of thephotoelectric conversion unit.

The amplifier circuit outputs a signal voltage in accordance with chargegenerated by the photoelectric conversion unit to the column signal linefor the column, and

the row scanning circuit supplies a control signal for controlling thereset circuit to the signal detection circuit.

According to the imaging device having the configuration 4, an organicCMOS image sensor capable of preventing random horizontal line noise canbe provided.

Configuration 5

An imaging device includes

a plurality of pixels arranged two-dimensionally, each including aphotoelectric conversion unit, an amplifier transistor having a gateconnected to the photoelectric conversion unit, and a feedback line thatelectrically connects a source of the amplifier transistor to thephotoelectric conversion unit,

a plurality of column signal lines each disposed for one of columns andconnected to the pixels disposed in the column,

a fourth switching circuit, and

first and second drain voltage applying circuits capable of beingelectrically connected to a drain of the amplifier transistor via thefourth switching circuit, where each of the first and second drainvoltage applying circuits generates a drain voltage of the amplifiertransistor.

The source of the amplifier transistor is electrically connected to acorresponding one of the column signal lines, and

the fourth switching circuit electrically connects one of the first andsecond drain voltage applying circuits to the drain of the amplifiertransistor for an odd numbered frame and electrically connects the otherof the first and second drain voltage applying circuits to the drain ofthe amplifier transistor for an even numbered frame.

The imaging device having Configuration 5 can prevent a variation of thedrain voltage of the amplifier transistor caused by, for example,disturbance noise or thermal noise.

Configuration 6

The imaging device having Configuration 5 further includes

first and second bias circuits disposed for one of the columns andcapable of being electrically connected to a plurality of load unitsconnected to the column signal line for the column, where each of thefirst and second bias circuits generates a control voltage that controlsthe load units, and

a fifth switching circuit that electrically connects one of the firstand second bias circuits to the load units for an odd numbered frame andelectrically connects the other of the first and second bias circuits tothe load units for an even numbered frame.

The imaging device having Configuration 6 can more effectively preventthe random horizontal line noise.

Configuration 7

In the imaging device of Configuration 2, 3, 5, or 6, the plurality ofcolumn signal lines include a first column signal line and a secondcolumn signal line disposed for each of the columns of the pixels.

At least some of the pixels in the same column are connected to thefirst column signal line, and the other pixels in the column areconnected to the second column signal line.

The imaging device of Configuration 7 can capture images at high framerate.

Configuration 8

In the imaging device of Configuration 7, at least some of the pixels inthe same column are pixels disposed in the odd numbered rows of theplurality of pixels, and

the other pixels in the column are pixels disposed in the even numberedrows of the plurality of pixels.

Configuration 9

In the imaging device of any one of Configurations 1 to 8, part of a rowscanning period for an odd numbered frame overlaps part of a rowscanning period for an even numbered frame.

The imaging device of Configuration 9 can capture images at high framerate.

Configuration 10

An imaging device includes

a plurality of pixels arranged two-dimensionally,

a row scanning circuit that generates a row scanning signal,

a plurality of reset voltage lines each disposed for one of rows andconnected to the pixels in the row,

first and second reset voltage generating circuits capable of beingelectrically connected to the pixels via the plurality of reset voltagelines, where each of the first and second reset voltage generatingcircuits generates a reset voltage, and

a first switching circuit that electrically connects one of the firstand second reset voltage generating circuits to the plurality of pixelsduring a row reset period and electrically connects the other of thefirst and second reset voltage generating circuits to the plurality ofpixels during a pixel signal readout period.

The imaging device having Configuration 10 can prevent a variation ofthe reset voltage caused by, for example, disturbance noise or thermalnoise.

Configuration 11

An imaging device includes

a plurality of pixels arranged two-dimensionally,

a row scanning circuit that generates a row scanning signal,

a plurality of column signal lines each disposed for one of columns andconnected to the pixels in the column,

a plurality of inverting amplifiers each disposed for one of the columnsand connected to the column signal line for the column,

a plurality of feedback signal lines each disposed for one of thecolumns and connected to an output terminal of the inverting amplifierfor the column,

first and second reference voltage applying circuits capable of beingelectrically connected to a reference voltage input terminal of each ofthe inverting amplifiers via a common reference voltage line, where eachof the first and second reference voltage applying circuits generates areference voltage for the inverting amplifiers, and

a second switching circuit that electrically connects one of the firstand second reference voltage applying circuits to the reference voltageinput terminals of the inverting amplifiers during a row reset periodand electrically connects the other of the first and second referencevoltage applying circuits to the reference voltage input terminals ofthe inverting amplifiers during a pixel signal readout period.

The imaging device having Configuration 11 can prevent a variation ofthe reference voltage caused by, for example, disturbance noise orthermal noise.

Configuration 12

The imaging device of Configuration 11 further includes

first and second bias circuits disposed for each of the columns andcapable of being electrically connected to a plurality of load unitsconnected to the column signal line for the column, where each of thefirst and second bias circuits generates a control voltage that controlsthe load units, and

a third switching circuit that electrically connects one of the firstand second bias circuits to the load units during the row reset periodand electrically connects the other of the first and second biascircuits to the load units during the pixel signal readout period.

The imaging device having Configuration 12 can prevent a variation ofthe bias voltage caused by, for example, disturbance noise or thermalnoise.

Configuration 13

In the imaging device of one of Configurations 10 to 12, each of theplurality of pixels includes a photoelectric conversion unit thatphotoelectrically converts incident light and a signal detection circuitincluding a reset circuit and an amplifier circuit, and the signaldetection circuit detects a signal of the photoelectric conversion unit.

The amplifier circuit outputs a signal voltage in accordance with chargegenerated by the photoelectric conversion unit to the column signal linefor the column, and

the row scanning circuit supplies a control signal for controlling thereset circuit to the signal detection circuit.

The imaging device having Configuration 13 can provide an organic CMOSimage sensor capable of preventing random horizontal line noise.

Configuration 14

An imaging device includes

a plurality of pixels arranged two-dimensionally, each including aphotoelectric conversion unit, an amplifier transistor having a gateconnected to the photoelectric conversion unit, and a feedback line thatelectrically connects a source of the amplifier transistor to thephotoelectric conversion unit,

a plurality of column signal lines each disposed for one of columns andconnected to the pixels disposed in the column,

a fourth switching circuit, and

first and second drain voltage applying circuits capable of beingelectrically connected to a drain of the amplifier transistor via thefourth switching circuit, where each of the first and second drainvoltage applying circuits generates a drain voltage of the amplifiertransistor.

The source of the amplifier transistor is electrically connected to acorresponding one of the column signal lines, and

the fourth switching circuit electrically connects one of the first andsecond drain voltage applying circuits to the drain of the amplifiertransistor during a row reset period and electrically connects the otherof the first and second drain voltage applying circuits to the drain ofthe amplifier transistor during a pixel signal readout period.

The imaging device having Configuration 14 can prevent a variation ofthe drain voltage of the amplifier transistor caused by, for example,disturbance noise or thermal noise.

Configuration 15

The imaging device according to Claim 14 further includes

first and second bias circuits disposed for one of the columns andcapable of being connected to a plurality of load units connected to acolumn signal line for the column, where each of the first and secondbias circuits generates a control voltage that controls the load units,and

a third switching circuit that electrically connects one of the firstand second bias circuits to the load units during the row reset periodand electrically connects the other of the first and second biascircuits to the load units during the pixel signal readout period.

The imaging device having Configuration 15 can more effectively preventthe random horizontal line noise.

Configuration 16

In the imaging device having any one of Configurations 3, 6, 12, and 15,each of the plurality of the load units includes a load transistor, andthe first and second bias circuits share the plurality of the loadtransistors.

Configuration 17

In the imaging device having any one of Configurations 11, 12, 14, and15, the plurality of column signal lines include a first column signalline and a second column signal line disposed for each of the columns ofthe pixels,

at least some of the pixels in the same column are connected to thefirst column signal line, and the other pixels in the column areconnected to the second column signal line.

Configuration 18

In the imaging device having Configuration 17, at least some of thepixels disposed in the same column are disposed in the odd numbered rowsof the plurality of pixels, and

the other pixels in the column are disposed in the even numbered rows ofthe plurality of pixels.

Configuration 19

In the imaging device having any one of Configurations 10, 11, 12, 13,14, 15, 17, and 18, part of the row reset period overlaps part of thepixel signal readout period.

The imaging device of Configuration 19 can capture images at high framerate.

Configuration 20

In the imaging device having Configuration 1 or 10, each of the firstand second reset voltage generating circuits includes a sample-and-holdcircuit.

Configuration 21

In the imaging device having any one of Configurations 3, 6, 12, 15, and16, each of the first and second bias circuits includes asample-and-hold circuit.

Configuration 22

In the imaging device having any one of Configurations 2, 3, 11, and 12,each of the first and second reference voltage applying circuitsincludes a sample-and-hold circuit.

Configuration 23

In the imaging device having any one of Configurations 5, 6, 14, and 15,each of the first and second drain voltage applying circuits includes asample-and-hold circuit.

According to the above-described aspects of the present disclosure,since the reset voltage can be held during one frame period (refer toFIG. 2), random horizontal line noise generated during the exposureperiod can be prevented while maintaining a high frame rate. As aresult, an imaging device capable of reducing image degradation can beprovided.

Exemplary embodiments of the present disclosure are described below withreference to the accompanying drawings. Note that modifications can beperformed within the scope and spirit of the disclosure as needed. Inaddition, one of the embodiments can be integrated with one or some ofthe other embodiments. In the following description, the same or similarconstituent elements are designated with the same reference numerals. Inthis case, description is not repeated again as needed. Additionally, inthe present specification, “A is electrically connected to B” meansstructures in which A is connected to B via one or more electricelements such as, for example, an inverting amplifier, a transistor, aswitching element or a source follower, as well as structures in which Ais directly connected to B by wiring.

First Exemplary Embodiment

The configuration and the functions of an imaging device according tothe first exemplary embodiment are described below with reference toFIGS. 3 to 6.

FIG. 3 is a schematic illustration of the circuit configuration of animaging device 1 according to the first exemplary embodiment. Note thatfour pixels 14 arranged in a 2×2 array are illustrated in FIG. 3. Inreality, millions of the pixels 14 are arranged in a two-dimensionalarray.

The imaging device 1 includes a plurality of the pixels 14, a drivecircuit unit, a photoelectric conversion unit control line 16, aplurality of vertical signal lines 17, and a power source wiring line21. The pixels 14 are arranged two-dimensionally, that is, arranged inthe row and column directions to form a photosensitive region (a pixelregion). The drive circuit unit sequentially drives the pixels 14 andreads out signal charge generated through photoelectric conversion. Notethat according to the present disclosure, the pixels 14 may beconfigured in a close-packed fashion (e.g., a configuration in which thepixels 14 are two-dimensionally arranged in a honeycomb structure).

The drive circuit unit includes, typically, a vertical scanning circuit15, a plurality of load units 18, a plurality of column signalprocessing circuits 19, a horizontal signal readout circuit 20, a biascircuit 40, and a reset voltage generating circuit 50. The verticalscanning circuit 15 is also referred to as a “row scanning circuit”. Thehorizontal signal readout circuit 20 is also referred to as a “columnscanning circuit”. The column signal processing circuit 19 is alsoreferred to as a “row signal accumulating circuit”.

Each of the pixels 14 includes the photoelectric conversion unit (alsoreferred to as “photoelectric converter”) 10 and a signal detectioncircuit. The signal detection circuit includes an amplifier transistor11, a reset transistor 12, and an address transistor 13. The addresstransistor is also referred to as a “row selection transistor”.

The photoelectric conversion unit 10 is electrically connected to adrain electrode of the reset transistor 12 and a gate electrode of theamplifier transistor 11 in the pixel 14 and photoelectrically convertslight incident on the pixel 14. The photoelectric conversion unit 10generates signal charge in accordance with the amount of the incidentlight and accumulates the signal charge.

The amplifier transistor 11 outputs a signal voltage in accordance withthe amount of the signal charge generated by the photoelectricconversion unit 10. The reset transistor 12 resets (initializes) thesignal charge in the photoelectric conversion unit 10. That is, thereset transistor 12 resets the voltage of the gate electrode of theamplifier transistor 11. In other word, the reset transistor 12 resets(initializes) the photoelectric conversion unit 10. The addresstransistor 13 selectively outputs the signal voltage from the pixel 14to the vertical signal line 17. In this manner, the output voltage ofthe amplifier transistor 11 is read out of the vertical signal line 17via the address transistor 13.

The vertical scanning circuit 15 generates a scanning signal. Thevertical scanning circuit 15 is electrically connected to the pixels 14disposed in each of the rows via a signal line corresponding to the row.The vertical scanning circuit 15 applies, to the gate electrodes of theaddress transistors 13, a row selection signal which controls on/off ofthe address transistors 13. In this manner, the rows are scanned in thecolumn direction to select the row which is a target of readout. Thesignal voltages are read out from the pixels 14 in the selected row tothe vertical signal lines 17. In addition, the vertical scanning circuit15 applies a signal voltage, which controls on/off of the resettransistors 12, to the gate electrodes of the reset transistors 12 via areset control line 24.

The photoelectric conversion unit control line 16 is commonly connectedto all the pixels 14. For example, the same positive constant voltage isapplied to all the photoelectric conversion units 10 in the imagingdevice 1 by the photoelectric conversion unit control line 16.

Each of the vertical signal lines 17 is provided so as to correspond toone of the rows of the pixels 14. The vertical signal line 17 isconnected to source electrodes of the address transistors 13 in thecorresponding row of the pixels 14. The vertical signal line 17transfers the signal voltage readout from the pixel 14 in the columndirection.

Each of the load units 18 (also referred to as “load circuit”) isdisposed so as to correspond to one of the columns. The load unit 18includes a load transistor (not illustrated). The load transistor istypically a MOS transistor. A drain electrode of the load transistor iselectrically connected to the vertical signal line 17 corresponding tothe column, and a source electrode of the load transistor is connectedto a reference voltage. In addition, gate electrodes of the loadtransistors in all of the columns are electrically connected to the biascircuit 40 via a common control line. The load unit 18 and the amplifiertransistor 11 form a source follower circuit. The load unit 18 functionsas a source follower current source. The amount of current of the loadunit 18 is adjusted by a voltage that the bias circuit 40 supplies.

Each of the column signal processing circuits 19 is disposed so as tocorrespond to one of the columns. The column signal processing circuit19 is electrically connected to the pixels 14 disposed in thecorresponding column via the vertical signal line 17 corresponding tothe column. The column signal processing circuit 19 performs, forexample, noise reduction signal processing (typically, correlated doublesampling) and analog-to-digital conversion (AD conversion).

The horizontal signal readout circuit 20 is electrically connected tothe plurality of column signal processing circuits 19. The horizontalsignal readout circuit 20 sequentially reads out the signals from thecolumn signal processing circuits 19 to a horizontal common signal line(not illustrated).

The power source wiring line 21 is a wiring line for the source followerpower source. The power source wiring line 21 supplies a predeterminedpower source voltage to the pixels 14. The power source wiring line 21is connected to the drain electrodes of the amplifier transistors 11.The same source follower power source voltage is applied to theamplifier transistors 11 of all the pixels 14 by the power source wiringline 21.

The bias circuit 40 typically includes a sample-and-hold circuit. Thebias circuit 40 generates a control voltage that controls on/off of theload transistors and applies the control voltage to the gate electrodesof the load transistors via a common control line.

The reset voltage generating circuit 50 is connected to the pixels 14via a reset voltage lines 25. The reset voltage generating circuit 50supplies, to the pixels 14, a reference voltage for resetting the FDs toa reference level.

In the imaging device 1, the pixels 14 in one row is sequentiallyselected by the vertical scanning circuit 15. The signal charge obtainedthrough photoelectric conversion performed by the photoelectricconversion unit 10 of a selected pixel 14 is amplified by the amplifiertransistor 11. The signal charge in the pixel 14 is read out into thevertical signal line 17 via the address transistor 13. The series ofoperations are repeatedly performed during each of horizontal scanningperiods in one frame scanning period.

Configuration and Operation of Reset Voltage Generating Circuit

FIG. 4A is a schematic illustration of an exemplary circuitconfiguration of the reset voltage generating circuit 50. An exemplaryconnection relationship between the reset voltage generating circuit 50and each of the reset voltage lines 25 corresponding to the (m−1)th rowto the (m+2)th row (m is an integer greater than or equal to 1) isillustrated in FIG. 4A.

The reset voltage generating circuit 50 includes a first switchingcircuit 51, a first reset voltage generating circuit 52, and a secondreset voltage generating circuit 53. The first reset voltage generatingcircuit 52 and the second reset voltage generating circuit 53 can beelectrically connected to the plurality of pixels 14 via the firstswitching circuit 51.

In the exemplary configuration illustrated in FIG. 4A, the firstswitching circuit 51 has two switches for each of the rows. For example,the (m−1)th row has a switch SWR_1[m−1] and a switch SWR_2[m−1] providedtherefor, where m is an integer greater than or equal to 1. The switchSWR_1[m−1] is connected to the first reset voltage generating circuit 52via a common signal line 56A. The switch SWR_2[m−1] is connected to thesecond reset voltage generating circuit 53 via a common signal line 56B.

Each of the first reset voltage generating circuit 52 and the secondreset voltage generating circuit 53 can include a sample-and-holdcircuit. In the illustrated example, the first reset voltage generatingcircuit 52 includes an output buffer 55A, a capacitor CAPR1, a switchSWR_SH_1, and a voltage control unit 54A. In contrast, the second resetvoltage generating circuit 53 includes an output buffer 55B, a capacitorCAPR2, a switch SWR_SH_2, and a voltage control unit 54B. The capacitorsCAPR1 and CAPR2 and the voltage control units 54A and 54B may bedisposed outside the imaging device 1.

Each of the voltage control units 54A and 54B generates the resetvoltage. The magnitudes of the reset voltages generated by the voltagecontrol units 54A and 54B are equivalent to each other. In other word,the magnitudes are equivalent to each other to the extent that the noisedue to the difference of these reset voltages cannot be recognized inthe resulting image. If the switch SWR_SH_1 is turned on, the outputvoltage from the voltage control unit 54A is charged in the capacitorCAPR1 as the reset voltage. This operation is referred to as “sampling”.If the switch SWR_SH_1 is turned off, the sample operation is completed,and sampled voltage signal is held by the capacitor CAPR1. Thisoperation is referred to as “hold”. As in the first reset voltagegenerating circuit 52, a sample-and-hold operation is performed in thesecond reset voltage generating circuit 53 by turning on and off theswitch SWR_SH_2.

As used herein, the phrase “causing the sample-and-hold circuit toperform the hold operation” is referred to as “enabling the circuit”. Inaddition, “causing the sample-and-hold circuit to perform the sampleoperation” is referred to as “disabling the circuit”. Furthermore, theholding period is referred to as an “enabled period”, and the samplingperiod is referred to as a “disabled period”.

The voltage signals held by the capacitors CAPR1 and CAPR2 are output tothe first switching circuit 51 via the output buffers 55A and 55B,respectively. The first switching circuit 51 can be controlled by, forexample, a peripheral logic circuit (not illustrated). The firstswitching circuit 51 performs exclusive control (or complementarycontrol) over the switches so that one of switches SWR_1[m−1] andSWR_2[m−1] is turned on and the other is turned off for a selected row.For an unselected row, each of switches SWR_1[m−1] and SWR_2[m−1] may beturned on or off.

If the switch SWR_1[m−1] is turned on and the switch SWR_2[m−1] isturned off, the first reset voltage generating circuit 52 iselectrically connected to the pixels 14 in the corresponding row (the(m−1)th row), and the reset voltage is supplied from the first resetvoltage generating circuit 52 to the pixels 14. In contrast, if theswitch SWR_1[m−1] is turned off and the switch SWR_2[m−1] is turned on,the second reset voltage generating circuit 53 is electrically connectedto the pixels 14 in the corresponding row (the (m−1)th row), and thereset voltage is supplied from the second reset voltage generatingcircuit 53 to the pixels 14. As illustrated in FIG. 4A, by providing theswitches SWR_1 and SWR_2 for each of the rows of the pixels 14, thecontrol that is more flexible than existing control can be provided and,thus, there are more choices than ever before for the driving method.

In the exemplary configuration illustrated in FIG. 4A, the reset voltagegenerating circuit 50 includes the first reset voltage generatingcircuit 52 and the second reset voltage generating circuit 53 eachhaving an independent voltage control unit. That is, as described abovewith reference to FIG. 4A, the first reset voltage generating circuit 52and the second reset voltage generating circuit 53 include the voltagecontrol unit 54A and the voltage control unit 54B, respectively.However, the configuration of the reset voltage generating circuit isnot limited to such an example.

FIG. 4B illustrates an example of the configuration of the reset voltagegenerating circuit including a single voltage control unit. Asillustrated in FIG. 4B, a reset voltage generating circuit 50D includesa first reset voltage generating circuit 52D and a second reset voltagegenerating circuit 53D each including a sample-and-hold circuit. Thefirst reset voltage generating circuit 52D includes the output buffer55A, the capacitor CAPR1, the switch SWR_SH_1, and a voltage controlunit 54D. The second reset voltage generating circuit 53D includes theoutput buffer 55B, the capacitor CAPR2, the switch SWR_SH_2, and thevoltage control unit 54D. That is, in this example, the voltage controlunit 54D is shared by the first reset voltage generating circuit 52D andthe second reset voltage generating circuit 53D. By allowing the firstreset voltage generating circuit 52D and the second reset voltagegenerating circuit 53D to share the voltage control unit 54D, the sizeof the drive circuit unit can be reduced, as compared with the case inwhich a plurality of voltage control units are provided. Like thevoltage control units 54A and 54B, the voltage control unit 54D may bedisposed inside the imaging device 1. Alternatively, the voltage controlunit 54D may be disposed outside the imaging device 1. As describedabove, the reset voltage may be generated by the shared voltage controlunit 54D.

One Frame Scanning Period Hold

FIG. 5 is an example of the drive timing diagram of the imaging device 1according to the present exemplary embodiment. In FIG. 5, one framescanning period is indicated by, for example, the arrow “FRAME n”, andthe timing of the row reset for each of the rows during one framescanning period is indicated by a diagonal dashed line, and the timingof signal readout for each of the rows is indicated by a diagonal solidline. The period of the row reset for each of the rows from the firstrow to the last row is defined as the row reset period, and the periodof the signal readout for each of the rows from the first row to thelast row is defined as the signal readout period. In the followingdescription, an n-th frame (frame n) represents an even numbered frame,and an (n+1)th frame (frame n+1) represents an odd numbered frame.

As used herein, a row from which the signal is to be read out isreferred to as a “READ row”, and a row to be subjected to row reset isreferred to as a “SHT row”. Each of the switches of the first switchingcircuit 51 is turned on if, for example, the control signal is “High”and is turned off if the control signal is “Low”. However, the polarityof the switch is not limited thereto. For example, the polarity of theswitch may be reversed. That is, when, for example, the (m−1)th row isdiscussed, the switches SWR_1[m−1] and SWR_2[m−1] may be controlled soas to be turned off when the control signal is “High” and be turned onwhen the control signal is “Low”. The first switching circuit 51electrically connects the first reset voltage generating circuit 52 tothe pixels 14 in the (m−1)th row if the switch SWR_1[m−1] is turned on.The first switching circuit 51 electrically connects the second resetvoltage generating circuit 53 to the pixels 14 in the (m−1)th row if theswitch SWR_2[m−1] is turned on. Although not illustrated, the controlsignal to control the switches SWR_1 and SWR_2 corresponding to anunselected row is fixed at “Low” or “High”.

In the example illustrated in FIG. 5, in the n-th frame scanning period,the control signal to control the switch SWR_2 for an SHT row is fixedat “High” during the row reset period. During the signal readout period,the control signal to control the switch SWR_2 for a READ row is fixedat “High”. As schematically indicated by the diagonal dashed lines andthe diagonal solid lines in FIG. 5, the SHT row and READ row are changedthroughout the rows from the first row to the last row due to scanningof the row that is the target of readout performed by the verticalscanning circuit 15.

As illustrated in FIG. 5, during the n-th frame scanning period, thecontrol signal to control the switch SWR_SH_2 of the second resetvoltage generating circuit 53 is fixed at “Low”, and the switch SWR_SH_2is turned off. Since the switch SWR_SH_2 is set to off, the voltagesignal held by the capacitor CAPR2 is supplied to the pixels 14 in theselected row via the first switching circuit 51 due to the holdoperation performed by the sample-and-hold circuit. In contrast, duringthe n-th frame scanning period other than the periods overlapping withthe (n−1)th frame scanning period and the (n+1)th frame scanning period,the control signal to control the switch SWR_SH_1 of the first resetvoltage generating circuit 52 is fixed at “High”, and the switchSWR_SH_1 is set to on. Since the switch SWR_SH_1 is set to on, the resetvoltage is charged in the capacitor CAPR1. That is, the sample-and-holdcircuit of the first reset voltage generating circuit 52 samples thevoltage signal in part of the n-th frame scanning period.

In contrast, in the (n+1)th frame scanning period, the control signal tocontrol the switch SWR_1 for a SHT row is fixed at “High” during the rowreset period. During the signal readout period, the control signal tocontrol the switch SWR_1 for a READ row is fixed at “High”. As describedabove, the SHT row and READ row change throughout the rows from thefirst row to the last row.

During the (n+1)th frame scanning period, the control signal to controlthe switch SWR_SH_1 of the first reset voltage generating circuit 52 isfixed at “Low”, and the switch SWR_SH_1 is turned off. Since the switchSWR_SH_1 is set to off, the voltage signal held by the capacitor CAPR1is supplied to the pixels 14 in the selected row via the first switchingcircuit 51 due to the hold operation performed by the sample-and-holdcircuit. In contrast, during the (n+1)th frame scanning period otherthan the periods overlapping with the n-th frame scanning period and the(n+2)th frame scanning period, the control signal to control the switchSWR_SH_2 of the second reset voltage generating circuit 53 is fixed at“High”, and the switch SWR_SH_2 is set to on. Since the switch SWR_SH_2is set to on, the reset voltage is charged in the capacitor CAPR2. Thatis, the sample-and-hold circuit of the first reset voltage generatingcircuit 52 samples the voltage signal in part of the n-th frame scanningperiod, while the sample-and-hold circuit of the second reset voltagegenerating circuit 53 samples the voltage signal in part of the (n+1)thframe scanning period.

According to the above-described driving method, the first reset voltagegenerating circuit 52 and the second reset voltage generating circuit 53can be alternately switched between the (n+1)th frame period and then-th frame period using the first switching circuit 51 and, thus, thepixels 14 in the READ row or the SHT row can be connected thereto.Since, according to the operation described with reference to FIG. 5,the hold operation performed by the sample-and-hold circuit can bemaintained throughout one frame scanning period, the variation of thereset voltage caused by, for example, disturbance noise or thermal noisecan be prevented. As a result, the random horizontal line noise can beeffectively reduced. Note that during the n-th frame scanning period,the first reset voltage generating circuit 52 may be enabled, and thesecond reset voltage generating circuit 53 may be disabled. During the(n+1)th frame scanning period, the first reset voltage generatingcircuit 52 may be disabled, and the second reset voltage generatingcircuit 53 may be enabled.

Row Reset Period Hold and Signal Readout Period Hold

A driving method that differs from the driving method illustrated inFIG. 5 is described below with reference to FIG. 6.

FIG. 6 is an example of a drive timing diagram of the imaging device 1other than that illustrated in FIG. 5 according to the present exemplaryembodiment. Although not illustrated, as in the example described withreference to FIG. 5, in this example, the control signal for each of theswitches SWR_1 and SWR_2 corresponding to an unselected row is fixed at“Low” or “High”.

According to the driving method, the first switching circuit 51electrically connects one of the first reset voltage generating circuit52 and the second reset voltage generating circuit 53 to the pixels 14in the selected row during the row reset period in one frame scanningperiod and electrically connects the other to the pixels 14 in theselected row during the pixel signal readout period in the one framescanning period.

In the example illustrated in FIG. 6, the control signal to control theswitch SWR_2 for a SHT row is set to “High” during the row reset periodin one frame scanning period. As a result, the pixels 14 (the pixels 14in the SHT row) are electrically connected to the second reset voltagegenerating circuit 53. At that time, the first reset voltage generatingcircuit 52 is electrically disconnected from the pixels 14 (the pixels14 in the SHT row).

As illustrated in FIG. 6, in this example, the control signal to controlthe switch SWR_SH_2 of the second reset voltage generating circuit 53 isfixed at “Low”. Accordingly, during the row reset period, the secondreset voltage generating circuit 53 is enabled. That is, since theswitch SWR_SH_2 is set to off, the reset voltage held in the capacitorCAPR2 through the hold operation performed by the sample-and-holdcircuit is supplied to the pixels 14 in the SHT row via the firstswitching circuit 51. In this example, by fixing the control signal tocontrol the switch SWR_SH_2 of the second reset voltage generatingcircuit 53 at “High” during a period other than the row reset period (aSHT blanking period bs), the capacitor CAPR2 of the second reset voltagegenerating circuit 53 is charged, that is, sampling is performed.

In contrast, the control signal to control the switch SWR_1 for a READrow is fixed at “High” during the signal readout period in the one framescanning period. As a result, the pixels 14 (the pixels 14 in the READrow) are electrically connected to the first reset voltage generatingcircuit 52. At that time, the second reset voltage generating circuit 53is electrically disconnected from the pixels 14 (the pixels 14 in theREAD row).

That is, in this example, the first reset voltage generating circuit 52is enabled during the signal readout period. That is, the control signalto control the switch SWR_SH_1 of the first reset voltage generatingcircuit 52 is fixed at “Low”. Accordingly, the switch SWR_SH_1 is set tooff. Thus, the reset voltage held in the capacitor CAPR1 through thehold operation performed by the sample-and-hold circuit is supplied tothe pixels 14 in the READ row via the first switching circuit 51. Inthis example, by fixing the control signal to control the switchSWR_SH_1 of the first reset voltage generating circuit 52 to “High”during a period other than the signal readout period (a READ blankingperiod br), the capacitor CAPR1 of the first reset voltage generatingcircuit 52 is charged, that is, sampling is performed.

According to the driving method, the hold operation performed by thesample-and-hold circuit of one of the first reset voltage generatingcircuit 52 and the second reset voltage generating circuit 53 can bemaintained during the entire row reset period and the entire signalreadout period. Unlike the hold during the entire one frame scanningperiod described with reference to FIG. 5, noise is inevitablygenerated. However, since the noise is equally distributed across allthe rows. As a result, the horizontal line noise is not detectable bythe eyes. This driving method is effective in a long exposure mode, suchas a mode used when the image of a starry sky is captured. Note that thefirst reset voltage generating circuit 52 may be enabled and the secondreset voltage generating circuit 53 may be disabled during the row resetperiod in the frame scanning period. In addition, the first resetvoltage generating circuit 52 may be disabled and the second resetvoltage generating circuit 53 may be enabled during the signal readoutperiod in the frame scanning period.

Second Exemplary Embodiment

A second exemplary embodiment of the present disclosure is describedbelow with reference to FIGS. 7 to 12. Unlike the imaging device 1according to the first exemplary embodiment, an imaging device accordingto the present exemplary embodiment includes a reference voltageapplying circuit 30 including a second switching circuit 62. The presentexemplary embodiment is applied to a reference voltage applying circuitof a column feedback structure. Hereinafter, description of aconstituent element that is the same as that of the imaging device 1according to the first exemplary embodiment is not repeated. Theconfiguration and the operation of the reference voltage applyingcircuit are mainly described below.

FIG. 7 is a schematic illustration of the circuit configuration of animaging device 1A according to a second exemplary embodiment of thepresent disclosure. FIG. 8A is a schematic illustration of a typicalexample of the circuit configuration of the reference voltage applyingcircuit 30 included in the imaging device 1A. An example of a connectionrelationship between the reference voltage applying circuit 30 and aninverting amplifier 22 for each of the i-th row and the (i+1)th row (iis an integer greater than or equal to 0) is illustrated in FIG. 8A.

As schematically illustrated in FIG. 7, the imaging device 1A includes aplurality of pixels 14, a drive circuit unit, a photoelectric conversionunit control line 16, a plurality of vertical signal lines 17, a powersource wiring line 21, and a plurality of feedback lines 23. In theexample of configuration illustrated in FIG. 7, the drive circuit unittypically includes a vertical scanning circuit 15, a plurality of loadunits 18, a plurality of column signal processing circuits 19, ahorizontal signal readout circuit 20, a plurality of the invertingamplifiers 22, the reference voltage applying circuit 30, and a biascircuit 40. Note that the inverting amplifier 22 is also referred to asa “feedback amplifier”.

Each of the inverting amplifiers 22 is disposed so as to correspond toone of the columns. A negative input terminal of the inverting amplifier22 is connected to a corresponding vertical signal line 17. A positiveinput terminal of the inverting amplifier 22 is electrically connectedto the reference voltage applying circuit 30 via a reference voltageline that is common to the columns of the pixels 14. In addition, theoutput terminal of the inverting amplifier 22 is connected to the drainsof the reset transistors 12 of the pixels 14 via a corresponding one ofthe feedback lines 23, each corresponding to one of the columns.

When the address transistor 13 and the reset transistor 12 are set toon, the inverting amplifier 22 receives the output of the addresstransistor 13 using the negative input terminal. That is, the invertingamplifier 22 performs a feedback operation so that the gate voltage ofthe amplifier transistor 11 is equal to a predetermined feedbackvoltage. Through the negative feedback control, thermal noise referredto as kTC noise and generated in the reset transistor 12 can beprevented.

The reference voltage applying circuit 30 typically includes asample-and-hold circuit. Sample-and-hold circuits typically include acapacitor. Sample-and-hold circuits sample and hold a predeterminedsignal voltage. The reference voltage applying circuit 30 applies areference voltage for the inverting amplifier 22 to the positive inputterminals of the inverting amplifiers 22 via a common reference voltageline. In a circuit configuration that is illustrated in FIG. 8A as anexample and that prevents thermal noise by negative feedback controlusing the inverting amplifier 22, the reference voltage is used as avoltage that determines the reference level of the FD of a pixel.Accordingly, to prevent random horizontal line noise, it is effective ifa variation of the reference voltage is prevented.

In the example of configuration illustrated in FIG. 8A, the referencevoltage applying circuit 30 includes a first reference voltage applyingcircuit 60, a second reference voltage applying circuit 61, and a secondswitching circuit 62. The first reference voltage applying circuit 60and the second reference voltage applying circuit 61 can be electricallyconnected to the positive input terminals of the inverting amplifiers 22via the second switching circuit 62.

In the example of configuration illustrated in FIG. 8A, the secondswitching circuit 62 includes a switch SWV_1 and a switch SWV_2 for eachof the columns. The switch SWV_1 for each of the columns is connected tothe first reference voltage applying circuit 60 via a common signal line63A. The switch SWV_2 for each of the columns is connected to the secondreference voltage applying circuit 61 via a common signal line 63B.

Each of the first reference voltage applying circuit 60 and the secondreference voltage applying circuit 61 can include a sample-and-holdcircuit. In the example illustrated in FIG. 8A, the first referencevoltage applying circuit 60 includes an output buffer 65A, a capacitorCAPV1, a switch SWV_SH_1, and a voltage control unit 64A. In contrast,the second reference voltage applying circuit 61 includes an outputbuffer 65B, a capacitor CAPV2, a switch SWV_SH_2, and a voltage controlunit 64B. The capacitors CAPV1 and CAPV2 and the voltage control units64A and 64B are disposed outside the imaging device 1A.

Each of the first reference voltage applying circuit 60 and the secondreference voltage applying circuit 61 generates a reference voltage forthe inverting amplifiers 22. The magnitudes of the reference voltagesgenerated by the first reference voltage applying circuit 60 and thesecond reference voltage applying circuit 61 are equivalent to eachother. In other word, the magnitudes are equivalent to each other to theextent that the noise due to the difference of these reference voltagescannot be recognized in the resulting image. If the switch SWV_SH_1 isturned on, the output voltage from the voltage control unit 64A ischarged in the capacitor CAPV1 as the reference voltage. This operationis referred to as “sampling”. If the switch SWV_SH_1 is turned off, thesample operation is completed, and sampled voltage signal is held by thecapacitor CAPV1. This operation is referred to as “hold”. As in thefirst reference voltage applying circuit 60, in the second referencevoltage applying circuit 61, by turning on and off the switch SWVSH_2, asample-and-hold operation is performed.

The voltage signals held by the capacitors CAPV1 and CAPV2 are output tothe second switching circuit 62 via the output buffers 65A and 65B,respectively. The second switching circuit 62 can be controlled by, forexample, a peripheral logic circuit (not illustrated). The secondswitching circuit 62 performs exclusive control over the switches sothat one of the switches SWV_1 and SWV_2 is turned on and the other isturned off.

If the switch SWV_1 is turned on and the switch SWV_2 is turned off, thefirst reference voltage applying circuit 60 is electrically connected tothe inverting amplifier 22 for the column for which the switch SWV_1 isturned on and, thus, the reference voltage is supplied from the firstreference voltage applying circuit 60 to the inverting amplifier 22. Incontrast, if the switch SWV_1 is turned off and the switch SWV_2 isturned on, the second reference voltage applying circuit 61 iselectrically connected to the inverting amplifiers 22 for the column forwhich the switch SWV_2 is turned on and, thus, the reference voltage issupplied from the second reference voltage applying circuit 61 to theinverting amplifiers 22.

In the example of configuration illustrated in FIG. 8A, the referencevoltage applying circuit 30 includes the first reference voltageapplying circuit 60 and the second reference voltage applying circuit 61each including an independent voltage control unit. However, theconfiguration is not limited to this example. For example, asillustrated in FIG. 8B, a reference voltage applying circuit 30Ddescribed below may be employed. That is, the reference voltage applyingcircuit 30D includes a first reference voltage applying circuit 60D anda second reference voltage applying circuit 61D which share a voltagecontrol unit 64D. Since the voltage control unit is shared, the size ofthe drive circuit unit can be reduced. The voltage control unit 64D maybe disposed either inside or outside the imaging device 1A.

One Frame Scanning Period Hold

FIG. 9 illustrates an example of a timing diagram of the imaging device1A according to the present exemplary embodiment. An HD signal in FIG. 9is a start pulse for a horizontal scanning signal. More specifically,FIG. 9 illustrates a typical example of the waveforms of control signalsfor the switches SWV_1 and SWV_2 in a period for which the n-th framescanning period overlaps the (n+1)th frame scanning period and itsvicinity when 10 rows are provided and the blanking period is set tohalf of one horizontal scanning period (1H period) and the exposureperiod is set to two horizontal scanning period (2H). Note that in ablanking period, no row reset and no signal readout are performed. FIG.10 illustrates the enabled period of each of the first reference voltageapplying circuit 60 and the second reference voltage applying circuit 61between two consecutive frames.

In the following description, it is assumed that the switches SWV_1 andSWV_2 of the second switching circuit 62 are turned on when the controlsignal is “High” and are turned off when the control signal is “Low”.However, the polarities of the switches are not limited thereto. Thepolarities of the switches may be reversed. That is, each of theswitches SWV_1 and SWV_2 may be driven so as to be turned off when thecontrol signal is “High” and be turned on when the control signal is“Low”.

The second switching circuit 62 electrically connects one of the firstreference voltage applying circuit 60 and the second reference voltageapplying circuit 61 to the plurality of inverting amplifiers 22 in therow reset period and the signal readout period according to the (n+1)thframe and electrically connects the other to the plurality of invertingamplifiers 22 in the row reset period and the signal readout periodaccording to the n-th frame.

In the example illustrated in FIG. 9, the control signal to control theswitch SWV_2 is fixed at “High”, and the control signal to control theswitch SWV_1 is fixed at “Low” in the row reset period and the signalreadout period according to the n-th frame. Thus, the second referencevoltage applying circuit 61 is electrically connected to the pluralityof inverting amplifiers 22, and the first reference voltage applyingcircuit 60 is electrically disconnected from the inverting amplifiers22. Note that in FIGS. 9 and 10, the waveforms of signals in the middle(“SWB_1”, “SWB_2”, “SWB_SH_1” and “SWB_SH_2”) are described in moredetail below.

As illustrated in FIG. 10, in the n-th frame scanning period, thecontrol signal to control the switch SWV_SH_2 of the second referencevoltage applying circuit 61 is fixed at “Low”, and the switch SWR_SH_2is turned off. Since the switch SWR_SH_2 is set to off, the voltagesignal held by the capacitor CAPV2 through the hold operation of thesample-and-hold circuit is supplied to the inverting amplifiers 22 viathe second switching circuit 62. In contrast, during the n-th framescanning period other than the periods overlapping with the (n−1)thframe scanning period and the (n+1)th frame scanning period, the controlsignal to control the switch SWV_SH_1 of the first reference voltageapplying circuit 60 is fixed at “High”, and the switch SWV_SH_1 is setto on. When the switch SWV_SH_1 is on, the reference voltage for theinverting amplifiers 22 is charged in the capacitor CAPV1. That is, thesample-and-hold circuit of the first reference voltage applying circuit60 samples the voltage signal in part of the n-th frame scanning period.

In contrast, in the row reset period and the signal readout periodaccording to the (n+1)th frame, the control signal to control the switchSWV_1 is fixed at “High”, and the control signal to control the switchSWV_2 is fixed at “Low”. Thus, the first reference voltage applyingcircuit 60 is electrically connected to the inverting amplifiers 22, andthe second reference voltage applying circuit 61 is electricallydisconnected from the inverting amplifiers 22. That is, the firstreference voltage applying circuit 60 is enabled, and the secondreference voltage applying circuit 61 is disabled.

As illustrated in FIG. 10, in the (n+1)th frame period, the controlsignal to control the switch SWV_SH_1 of the first reference voltageapplying circuit 60 is fixed at “Low”, and the switch SWVSH_1 is turnedoff. Since the switch SWV_SH_1 is off, the voltage signal held by thecapacitor CAPV1 through the hold operation performed by thesample-and-hold circuit is supplied to the inverting amplifiers 22 viathe second switching circuit 62. In contrast, during the (n+1)th framescanning period other than the periods overlapping with the n-th framescanning period and the (n+2)th frame scanning period, the controlsignal to control the switch SWR_SH_2 of the first reset voltagegenerating circuit 61 is fixed at “High”, and the switch SWR_SH_2 is setto on. When the switch SWV_SH_2 is on, the reference voltage for theinverting amplifiers 22 is charged in the capacitor CAPV2. That is, thesample-and-hold circuit of the second reference voltage applying circuit61 samples the voltage signal in part of the (n+1)th frame scanningperiod.

As illustrated in FIG. 9, in this example, the row reset (the row resetserving as an electronic shutter) for the first row of the (n+1)th frameis started before completion of signal readout for the 10th row of then-th frame. That is, in this example, there is an overlapping periodbetween two consecutive frame scanning periods.

In the example illustrated in FIGS. 9 and 10, the second referencevoltage applying circuit 61 is connected to the inverting amplifiers 22during a signal readout period according to the n-th frame in theoverlapping period. In addition, the first reference voltage applyingcircuit 60 is connected to the inverting amplifiers 22 during the rowreset period according to the (n+1)th frame. While the example has beendescribed with reference to the overlapping period that is set to 2HD,the length of the overlapping period can be changed in accordance withthe control of the exposure period.

In addition, the switch SWVSH_1 and the switch SWV_SH_2 are set to offduring the overlapping period. In this manner, the first referencevoltage applying circuit 60 and the second reference voltage applyingcircuit 61 are enabled and, thus, the reference voltage is supplied fromeach of the first reference voltage applying circuit 60 and the secondreference voltage applying circuit 61 to the second switching circuit62.

As described with reference to FIG. 1, the signal readout period (theperiod from the time t3 to the time t4 in FIG. 1) can include a periodfor resetting the FD to read out the reference level (“ED RESET” in FIG.1). In a configuration such as a configuration that is illustrated inFIG. 8A and that can prevent thermal noise through negative feedbackcontrol using the inverting amplifier 22, the FD reset period caninclude a period for forming a feedback path including the invertingamplifier 22 as part of the path. The FD reset can be performed duringthe period of the electronic shutter (the period from the time t1 to thetime t2 in FIG. 1) in addition to during the signal readout period.According to the driving method described with reference to FIGS. 9 and10, by using the second switching circuit 62, the first referencevoltage applying circuit 60 and the second reference voltage applyingcircuit 61 can be alternately connected to the inverting amplifiers 22between the row reset period and the signal readout period according tothe (n+1)th frame and the row reset period and the signal readout periodaccording to the n-th frame. That is, the signal voltage sampled intothe capacitor CAPV2 of the second reference voltage applying circuit 61can be used for two FD reset operations performed for each of the rowsaccording to the n-th frame. In contrast, the signal voltage sampledinto the capacitor CAPV1 of the first reference voltage applying circuit60 can be used for two FD reset operations performed for each of therows according to the (n+1)th frame.

According to the operation described with reference to FIGS. 9 and 10,the hold operation performed by the sample-and-hold circuit can bemaintained throughout one frame scanning period. Accordingly, avariation of the reference voltage caused by disturbance noise orthermal noise can be prevented. As a result, random horizontal linenoise can be effectively prevented.

Row Reset Period Hold and Signal Readout Period Hold

A driving method that differs from the driving method illustrated inFIGS. 9 and 10 is described below with reference to FIGS. 11 and 12.

FIG. 11 illustrates another example of control timing of the switches ofthe second switching circuit 62 of the imaging device 1A according tothe present exemplary embodiment. FIG. 12 illustrates an example ofcontrol timing of the switches of the reference voltage applying circuit30 according to two consecutive frames. In addition, FIG. 12 illustratesthe period in which each of the first reference voltage applying circuit60 and the second reference voltage applying circuit 61 is enabled. Thewaveforms of signals illustrated in the middle of FIGS. 11 and 12(“SWB_1” and “SWB_2”) are described in more detail below.

According to the driving method, the second switching circuit 62electrically connects one of the first reference voltage applyingcircuit 60 and the second reference voltage applying circuit 61 to theinverting amplifiers 22 during the row reset period in one frame periodand electrically connects the other to the inverting amplifiers 22during the pixel signal readout period.

In an example illustrated in FIG. 11, the row reset and the signalreadout are serially performed. For example, during the row reset periodin each of the frame periods, the control signal to control the switchSWV_2 is fixed at “High”. As a result, the inverting amplifiers 22 areelectrically connected to the second reference voltage applying circuit61. At that time, the first reference voltage applying circuit 60 iselectrically disconnected from the inverting amplifiers 22.

As illustrated in FIG. 12, in this example, the control signal tocontrol the switch SWV_SH_2 of the second reference voltage applyingcircuit 61 is fixed at “Low”. Accordingly, the second reference voltageapplying circuit 61 is enabled during the row reset period. That is,since the switch SWV_SH_2 is off, the voltage signal held by thecapacitor CAPV2 through the hold operation performed by thesample-and-hold circuit is supplied to the inverting amplifiers 22 viathe second switching circuit 62. In this example, by fixing the controlsignal to control the switch SWV_SH_2 at “High”, charging of thecapacitor CAPV2, that is, sampling is performed.

In contrast, during the signal readout period in each of the frameperiods, the control signal to control the switch SWV_1 is fixed at“High” (refer to, for example, FIG. 11). As a result, the invertingamplifiers 22 are electrically connected to the first reference voltageapplying circuit 60. At that time, the second reference voltage applyingcircuit 61 is electrically disconnected from the inverting amplifiers22.

That is, in this example, the first reference voltage applying circuit60 is enabled during the signal readout period. That is, the controlsignal to control the switch SWV_SH_1 is fixed at “Low” and, thus, theswitch SWV_SH_1 is off. Accordingly, the voltage signal held by thecapacitor CAPV1 through the hold operation performed by thesample-and-hold circuit is supplied to the inverting amplifiers 22 viathe second switching circuit 62. In this example, by fixing the controlsignal to control the switch SWVSH_1 at “High” during a period otherthan the signal readout period, charging of the capacitor CAPV1, thatis, sampling is performed.

As can be seen from FIG. 12, in this example, the switch SWV_SH_1 andthe switch SWV_SH_2 are turned off during the overlapping period forwhich two consecutive frame scanning periods overlap each other. In thismanner, each of the first reference voltage applying circuit 60 and thesecond reference voltage applying circuit 61 is enabled, and thereference voltage is supplied from each of the first reference voltageapplying circuit 60 and the second reference voltage applying circuit 61to the second switching circuit 62.

According to the driving method, the hold operation performed by thesample-and-hold circuit of one of the first reference voltage applyingcircuit 60 and the second reference voltage applying circuit 61 can bemaintained throughout the row reset period and throughout the signalreadout period. Unlike the hold throughout the one frame scanning perioddescribed with reference to FIGS. 9 and 10, noise is inevitablygenerated. However, since the noise is equally distributed across allthe rows. As a result, the horizontal line noise is not detectable bythe eyes. This driving method is effective in a long exposure mode, suchas a mode used when the image of a starry sky is captured.

Third Exemplary Embodiment

A third exemplary embodiment of the present disclosure is describedbelow with reference to FIGS. 9 to 12 and FIGS. 13A and 13B. Unlike theimaging device 1 according to the first exemplary embodiment, theimaging device according to the present exemplary embodiment includes areference voltage applying circuit 30 including a second switchingcircuit 62 and a bias circuit 40A including a third switching circuit72. The present exemplary embodiment is applied to a reference voltageapplying circuit and a bias circuit having a column feedbackconfiguration. The configuration and the operation of the referencevoltage applying circuit 30 are the same as those described in thesecond exemplary embodiment. The configuration and the operation of thebias circuit are mainly described below.

FIG. 13A is a schematic illustration of the circuit configuration of animaging device 1B according to the third exemplary embodiment of thepresent disclosure. An exemplary connection relationship between thebias circuit 40A including the third switching circuit 72 and the loadunit 18 for each of the i-th and (i+1)th columns is illustrated in FIG.13A. A connection relationship between each of the wiring lines and eachof the transistors in the pixels 14 is the same as that illustrated inFIG. 7.

In the example of configuration illustrated in FIG. 13A, the biascircuit 40A includes a first bias circuit 70, a second bias circuit 71,and a third switching circuit 72. The first bias circuit 70 and thesecond bias circuit 71 can be electrically connected to the load units18 via the third switching circuit 72.

In the configuration illustrated in FIG. 13A, the third switchingcircuit 72 has a switch SWB_1 and a switch SWB_2 for each of thecolumns. The switch SWB_1 for each of the columns is connected to thefirst bias circuit 70 via a common signal line 73A. The switch SWB_2 foreach of the columns is connected to the second bias circuit 71 via acommon signal line 73B.

Each of the first bias circuit 70 and the second bias circuit 71 caninclude a sample-and-hold circuit. In the example illustrated in FIG.13A, the first bias circuit 70 includes an output buffer 75A, acapacitor CAPB1, a switch SWB_SH_1, and a voltage control unit 74A. Incontrast, the second bias circuit 71 includes an output buffer 75B, acapacitor CAPB2, a switch SWB_SH_2, and a voltage control unit 74B. Thecapacitors CAPB1 and CAPB2 and the voltage control units 74A and 74B maybe disposed outside the imaging device 1B.

Each of the first bias circuit 70 and the second bias circuit 71generates a control voltage for controlling on/off of the loadtransistor of the load unit 18. The magnitudes of the control voltagesgenerated by the first bias circuit 70 and the second bias circuit 71are equivalent to each other. In other word, the magnitudes areequivalent to each other to the extent that the noise due to thedifference of these control voltages cannot be recognized in theresulting image. If the switch SWB_SH_1 is turned on, the output voltageoutput from the voltage control unit 74A is charged in the capacitorCAPB1 as the control voltage. This operation is referred to as“sampling”. If the switch SWB_SH_1 is turned off, the sample operationis completed, and sampled voltage signal is held by the capacitor CAPB1.This operation is referred to as “hold”. As in the first bias circuit70, in the second bias circuit 71, by turning on and off the switchSWB_SH_2, a sample-and-hold operation is performed.

The voltage signals held by the capacitors CAPB1 and CAPB2 are output tothe third switching circuit 72 via the output buffers 75A and 75B,respectively. The third switching circuit 72 can be controlled by, forexample, a peripheral logic circuit (not illustrated). The thirdswitching circuit 72 performs exclusive control over the switches sothat one of the switches SWB_1 and SWB_2 is turned on and the other isturned off.

If the switch SWB_1 is turned on and the switch SWB_2 is turned off, thefirst bias circuit 70 is electrically connected to the load unit 18 forthe column for which the switch SWB_1 is turned on and, thus, thecontrol voltage is supplied from the first bias circuit 70 to the loadunits 18. In contrast, if the switch SWB_1 is turned off and the switchSWB_2 is turned on, the second bias circuit 71 is electrically connectedto the load unit 18 for the column for which the switch SWB_2 is turnedon and, thus, the control voltage is supplied from the second biascircuit 71 to the load unit 18. In the example of configurationillustrated in FIG. 13A, the load unit 18 of each of the columns iselectrically connected to the inverting amplifier 22 for the column viaa vertical signal line. Accordingly, by preventing a variation of thecontrol signal to control on/off of the load transistor, randomhorizontal line noise can be more effectively prevented.

As illustrated in FIG. 13B, a bias circuit 40D including a first biascircuit 70D and a second bias circuit 71D that share a voltage controlunit 74D may be employed. Since the voltage control unit is shared, thesize of the drive circuit unit can be advantageously reduced. Thevoltage control unit 74D may be disposed either inside or outside theimaging device 1B.

One Frame Period Hold

Refer back to FIGS. 9 and 10 again. The signal waveforms of the switchesof the first bias circuit 70, the second bias circuit 71, and the thirdswitching circuit 72 are also illustrated in FIGS. 9 and 10. Thefollowing description is given on the assumption that each of theswitches SWB_1 and SWB_2 of the third switching circuit 72 is turned onwhen the control signal is “High” and is turned off when the controlsignal is “Low”. However, the polarities of the switches are not limitedthereto. The polarities of the switches may be reversed.

As described above, according to the driving method illustrated in FIGS.9 and 10, the second switching circuit 62 electrically connects one ofthe first reference voltage applying circuit 60 and the second referencevoltage applying circuit 61 to the inverting amplifiers 22 in the rowreset period and the signal readout period according to the (n+1)thframe and electrically connects the other to the inverting amplifiers 22in the row reset period and the signal readout period according to then-th frame. In addition, according to the driving method describedherein, the third switching circuit 72 electrically connects one of thefirst bias circuit 70 and the second bias circuit 71 to the loadtransistors in the row reset period and the signal readout periodaccording to the (n+1)th frame and electrically connects the other tothe load transistors in the row reset period and the signal readoutperiod according to the n-th frame.

As can be seen from FIG. 9, the control signal to control the switchSWB_2 is fixed at “High” and the control signal to control the switchSWB_1 is fixed at “Low” in the row reset period and the signal readoutperiod according to the n-th frame. Thus, the second bias circuit 71 iselectrically connected to the load units 18, and the first bias circuit70 is electrically disconnected from the load units 18.

As can be seen from FIG. 10, the control signal to control the switchSWB_SH_2 is fixed at “Low” during the n-th frame scanning period and,thus, the switch SWB_SH_2 is turned off. Accordingly, the voltage signalheld by the capacitor CAPB2 through the hold operation performed by thesample-and-hold circuit is supplied to the load units 18 via the thirdswitching circuit 72. At that time, by fixing the control signal tocontrol the switch SWB_SH_1 at “High”, the switch SWB_SH_1 is turned on.Since the switch SWB_SH_1 is turned on, the reset voltage is charged inthe capacitor CAPB1. That is, the sample-and-hold circuit of the firstbias circuit 70 performs sampling of the voltage signal during the n-thframe scanning period other than the periods overlapping with the(n−1)th frame scanning period and the (n+1)th frame scanning period.

In contrast, in the row reset period and the signal readout periodaccording to the (n+1)th frame, the control signal to control the switchSWB_1 is fixed at “High”, and the control signal to control the switchSWB_2 is fixed at “Low” (refer to FIG. 9). Thus, the first bias circuit70 is electrically connected to the load units 18, and the second biascircuit 71 is electrically disconnected from the load units 18.

As illustrated in FIG. 10, during the (n+1)th frame scanning period, thecontrol signal to control the switch SWB_SH_1 is fixed at “Low” and,thus, the switch SWB_SH_1 is turned off. Accordingly, the voltage signalheld by the capacitor CAPB1 through the hold operation performed by thesample-and-hold circuit is supplied to the load units 18 via the thirdswitching circuit 72. In contrast, the switch SWB_SH_2 is turned on byfixing the control signal at “High”. When the switch SWB_SH_2 is on, thecontrol voltage is charged in the capacitor CAPB2. That is, thesample-and-hold circuit of the second bias circuit 71 samples thevoltage signal during the (n+1)th frame scanning period other than theperiods overlapping with the n-th frame scanning period and the (n+2)thframe scanning period.

In the example illustrated in FIG. 9, there is an overlapping periodbetween two consecutive frame scanning periods. The second bias circuit71 is connected to the load units 18 during a signal readout periodaccording tor the n-th frame in the overlapping period. In addition, thefirst bias circuit 70 is connected to the load units 18 during the rowreset period according to the (n+1)th frame.

Note that during the overlapping period, the switch SWB_SH_1 and theswitch SWB_SH_2 are turned off. In this manner, the first bias circuit70 and the second bias circuit 71 are enabled and, thus, the referencevoltage is supplied to the third switching circuit 72 from each of thefirst bias circuit 70 and the second bias circuit 71.

According to the driving method described with reference to FIGS. 9 and10, by using the second switching circuit 62 and the third switchingcircuit 72, the first reference voltage applying circuit 60 and thesecond reference voltage applying circuit 61 can be alternatelyconnected to the inverting amplifiers 22 between the row reset periodand the signal readout period according to the (n+1)th frame and the rowreset period and the signal readout period according to the n-th frame.In addition, the first bias circuit 70 and the second bias circuit 71can be alternately connected to the load units 18. According to theoperation described with reference to FIGS. 9 and 10, the hold operationperformed by the sample-and-hold circuit can be maintained throughoutone frame scanning period. Accordingly, a variation of the referencevoltage caused by disturbance noise or thermal noise can be prevented.As a result, random horizontal line noise can be effectively prevented.

Row Reset Period Hold and Signal Readout Period Hold

Referring back to FIGS. 11 and 12, a driving method that differs fromthe driving method illustrated in FIGS. 9 and 10 is described below.

The signal waveforms of the switches of the first bias circuit 70, thesecond bias circuit 71, and the third switching circuit 72 are alsoillustrated in FIGS. 11 and 12. As described above, in the drivingmethod illustrated in FIGS. 11 and 12, the second switching circuit 62electrically connects one of the first reference voltage applyingcircuit 60 and the second reference voltage applying circuit 61 to theinverting amplifiers 22 during the row reset period in one frame periodand electrically connects the other to the inverting amplifiers 22during the pixel signal readout period. In addition, in the drivingmethod described herein, the third switching circuit 72 electricallyconnects one of the first bias circuit 70 and the second bias circuit 71to the load transistors during the row reset period and electricallyconnects the other to the load transistors during the pixel signalreadout period.

In the example illustrated in FIG. 11, the row reset and the signalreadout are serially performed. For example, during the row reset periodin each of the frame periods, the control signal to control the switchSWB_2 is fixed at “High”. As a result, the load units 18 areelectrically connected to the second bias circuit 71. At that time, thefirst bias circuit 70 is electrically disconnected from the load units18.

As illustrated in FIG. 12, in this example, the control signal tocontrol the switch SWB_SH_2 of the second bias circuit 71 is fixed at“Low”. Accordingly, the second bias circuit 71 is enabled during the rowreset period. That is, since the switch SWB_SH_2 is off, the voltagesignal held by the capacitor CAPB2 through the hold operation performedby the sample-and-hold circuit is supplied to the load units 18 via thethird switching circuit 72. In this example, by fixing the controlsignal to control the switch SWB_SH_2 at “High”, charging of thecapacitor CAPB2, that is, sampling is performed.

In contrast, during the signal readout period in each of the frameperiods, the control signal to control the switch SWB_1 is fixed at“High” (refer to, for example, FIG. 11). As a result, the load units 18are electrically connected to the first bias circuit 70. At that time,the second bias circuit 71 is electrically disconnected from the loadunits 18.

That is, in this example, the first bias circuit 70 is enabled duringthe signal readout period. That is, the control signal to control theswitch SWB_SH_1 of the first bias circuit 70 is fixed at “Low” and,thus, the switch SWB_SH_1 is off. Accordingly, the voltage signal heldby the capacitor CAPB1 through the hold operation performed by thesample-and-hold circuit is supplied to the load units 18 via the thirdswitching circuit 72. In this example, by fixing the control signal tocontrol the switch SWB_SH_1 at “High” during a period other than thesignal readout period, charging of the capacitor CAPB1, that is,sampling is performed.

As can be seen from FIG. 12, in this example, the switch SWB_SH_1 andthe switch SWB_(—) SH_2 are turned off during the overlapping period inwhich two consecutive scanning frames overlap each other. In thismanner, each of the first bias circuit 70 and the second bias circuit 71is enabled, and the control voltage to control the load transistor issupplied from each of the first bias circuit 70 and the second biascircuit 71 to the third switching circuit 72.

According to the driving method, the hold operation performed by thesample-and-hold circuit of one of the first bias circuit 70 and thesecond bias circuit 71 can be maintained throughout the row reset periodand throughout the signal readout period. Unlike the hold throughout theone frame scanning period described with reference to FIGS. 9 and 10,noise is inevitably generated. However, since the noise is equallydistributed across all the rows. As a result, the horizontal line noiseis not detectable by the eyes. This driving method is effective in along exposure mode, such as a mode used when the image of a starry skyis captured.

Fourth Exemplary Embodiment

An imaging device according to a fourth exemplary embodiment of thepresent disclosure is described below with reference to FIGS. 10, 14 and15. Unlike the imaging device 1A according to the second exemplaryembodiment, the imaging device according to the present exemplaryembodiment has two column signal lines for each of the columns of thepixels 14. When a given column is discussed, at least some of the pixels14 in the column are connected to a first column signal line, which isone of two column signal lines provided for the column. The other pixels14 in the column are connected to a second column signal line, which isthe other column signal line provided for the column. That is, in theimaging device according to the present exemplary embodiment, the outputof the at least some of the pixels 14 are read out via the first columnsignal line, and the outputs of the other pixels 14 are read out via thesecond column signal line.

As described below with reference to the accompanying drawings,typically, at least one of the pixels 14 arranged in an odd numbered rowis connected to the first column signal line, and at least one of thepixels 14 arranged in an even numbered row is connected to the secondcolumn signal line. Like the second exemplary embodiment, the presentexemplary embodiment is applicable to reference voltage applyingcircuits of a column feedback configuration. The differences from theimaging device 1A according to the second exemplary embodiment aremainly described below.

FIG. 14 is a schematic illustration of the circuit configuration of animaging device 1C according to the fourth exemplary embodiment of thepresent disclosure. In FIG. 14, four pixels in a given column among aplurality of pixels 14 arranged two-dimensionally are illustrated. Inthe example of configuration, the imaging device 1C includes a pluralityof vertical signal lines 17A each connected to the pixels 14 arranged inone of the odd numbered rows and a plurality of vertical signal lines17B each connected to the pixels 14 arranged in one of the even numberedrows.

In this example, the imaging device 1C further includes a plurality offeedback lines. Two of the feedback lines are disposed for each of thecolumns of the pixels 14. When a given column of the pixels 14 isdiscussed, feedback lines 23A and 23B are individually provided, asillustrated in FIG. 14. In this example, the feedback line 23A iselectrically connected to the pixels 14 disposed in odd numbered rows,and the feedback lines 23B is electrically connected to the pixels 14disposed in even numbered rows. Note that for convenience ofdescription, in FIG. 14, one of two pairs each consisting of thevertical signal line and the feedback line (the pair consisting of thevertical signal line 17B and the feedback line 23B), which is providedfor a given column of the pixels 14, is referred to as a “column i”, andthe other pair (the pair consisting of the vertical signal line 17A andthe feedback line 23A) is referred to as a “column i+1”. The same mayapply to other drawings described below to distinguish the pairsconsisting of a vertical signal line and a feedback line disposed in thesame column from one another.

In the example of configuration illustrated in FIG. 14, the imagingdevice 1C includes a reference voltage applying circuit 30B including afirst reference voltage applying circuit 60, a second reference voltageapplying circuit 61, and a second switching circuit 62A. The secondswitching circuit 62A has two pairs of switches each for one of thecolumns of the pixels 14. In this example, a switch SWV_21 is connectedbetween the positive input terminal of the inverting amplifier 22 havingan output terminal connected to the feedback line 23A and a signal line63A, and a switch SWV_22 is connected between the input terminal and asignal line 63B. In addition, a switch SWV_11 is connected between thepositive input terminal of the inverting amplifier 22 having an outputterminal connected to the feedback line 23B and the signal line 63A, anda switch SWV_12 is connected between the input terminal and the signalline 63B. As illustrated in FIG. 14, the switch SWV_11 and the switchSWV_21 each corresponding to one of the columns are connected to thefirst reference voltage applying circuit 60 via the common signal line63A. The switch SWV_12 and the switch SWV_22 each corresponding to oneof the columns are connected to the second reference voltage applyingcircuit 61 via the common signal line 63B.

Like the above-described pair consisting of the switches SWV_1 and SWV_2of the second switching circuit 62, exclusive control is performed overthe pair consisting of the switches SWV_11 and SWV_12 of the secondswitching circuit 62A. For example, when the switch SWV_11 is set to on,the switch SWV_12 is set to off. The same operation is performed overthe pair consisting of the switches SWV_21 and SWV_22 of the secondswitching circuit 62A.

One Frame Scanning Period Hold

FIG. 15 illustrates an example of the control timing of the switches ofthe second switching circuit 62A in the imaging device 1C according tothe present exemplary embodiment.

According to the driving method, row reset is performed using one of thevertical signal line 17A and the vertical signal line 17B provided foreach of the columns. At the same time, signal readout is performed usingthe other of the vertical signal line 17A and the vertical signal line17B. As in the example illustrated in FIG. 9, even in the exampleillustrated in FIG. 15, there is an overlapping period between twoconsecutive frame scanning periods. In the example of timing illustratedin FIG. 15, the overlapping period includes two 1H periods. In theexample of timing illustrated in FIG. 15, signal readout and row resetare performed using the vertical signal line 17B and the vertical signalline 17A, respectively, in the first one of the two 1H periods. In thenext 1H period, signal readout and row reset are performed using thevertical signal line 17A and the vertical signal lines 17B,respectively. Note that signal waveforms illustrated in the middle ofFIG. 15 (“SWB_11”, “SWB_12”, “SWB_21”, and “SWB_22”) are described indetail below.

In the example illustrated in FIG. 15, the control signals for theswitches SWV_12 and SWV_22 connected to the signal line 63B are set to“High” in the row reset period and the signal readout period accordingto the n-th frame. Thus, the inverting amplifiers 22 are electricallyconnected to the second reference voltage applying circuit 61. Incontrast, the switch SWV_11 and SWV_21 connected to the signal line 63Aare set to “Low”. Thus, the first reference voltage applying circuit 60is electrically disconnected from the inverting amplifiers 22.

Control of the switch SWV_SH_1 and the switch SWVSH_2 can be the same asin the example illustrated in FIG. 10. As illustrated in FIG. 10, thecontrol signal to control the switch SWV_SH_2 is fixed at “Low” in then-th frame scanning period and, thus, the switch SWV_SH_2 is turned off.At that time, the voltage signal held by the capacitor CAPV2 through thehold operation performed by the sample-and-hold circuit is supplied tothe inverting amplifiers 22 via the second switching circuit 62A. Incontrast, the switch SWV_SH_1 is turned on by fixing the control signalat “High”. When the switch SWV_SH_1 is on, the reference voltage for theinverting amplifier 22 is charged in the capacitor CAPV1.

As illustrated in FIG. 15, in the row reset period and the signalreadout period according to the (n+1)th frame, the control signals forthe switches SWV_12 and SWV_22 are set to “Low” to electricallydisconnect the second reference voltage applying circuit 61 from theinverting amplifiers 22. In addition, the control signals for theswitches SWV_11 and SWV_21 are set to “High” to electrically connect thefirst reference voltage applying circuit 60 to the inverting amplifiers22.

Referring back to FIG. 10, the control signal to control the switchSWV_SH_1 is fixed at “Low” during the (n+1)th frame scanning period and,thus, the switch SWV_SH_1 is turned off. At that time, the voltagesignal held by the capacitor CAPV1 through the hold operation performedby the sample-and-hold circuit is supplied to the inverting amplifiers22 via the second switching circuit 62A. In contrast, the switchSWV_SH_2 is turned on by fixing the control signal to control the switchSWV_SH_2 at “High”. When the switch SWV_SH_2 is on, the referencevoltage for the inverting amplifier 22 is charged in the capacitorCAPV2.

As described above, in this example, there is an overlapping periodbetween two consecutive frame scanning periods, and the overlappingperiod includes two 1H periods. The first 1H period is discussed belowfirst. In the first 1H period, signal readout for the n-th frame isperformed using the vertical signal lines 17B. That is, among the pixels14 in the even numbered rows, the output of the pixels 14 in a selectedrow is read out via the vertical signal line 17B.

As described above, the signal readout period can include a period forresetting an FD for reading out the reference level. A feedback path isformed during the FD reset period by turning on the amplifier transistor11 and the reset transistor 12 in the pixel 14. That is, the feedbackpath includes the vertical signal line and the feedback line as part ofthe path. Accordingly, in, as illustrated in FIG. 8A, the circuitconfiguration in which one vertical signal line 17 and one feedback line23 are disposed for each of the columns, formation of a feedback pathfor FD reset serving as an electronic shutter and formation of afeedback path for FD reset for the reference level readout cannot beperformed at the same time.

In contrast, according to the circuit configuration of the fourthexemplary embodiment of the present disclosure, two vertical signallines (the vertical signal lines 17A and 17B) and two invertingamplifiers 22 are disposed for each of the columns of the pixels 14.Accordingly, a feedback circuit for FD reset to read out the referencelevel can be formed for the pixel 14 connected to the vertical signallines 17B at the same time as a feedback circuit for FD reset serving asan electronic shutter for the pixel 14 connected to the vertical signalline 17A for the same column is formed.

As described above, in this example, during the first 1H period of theoverlapping period, signal readout is performed for the n-th frame usingthe vertical signal line 17B. As illustrated in FIG. 15, during the 1Hperiod, the control signal to control the switch SWV_12 is set to“High”. Accordingly, the second reference voltage applying circuit 61 iselectrically connected to the inverting amplifier 22 connected to thevertical signal line 17B. As illustrated in FIG. 10, the secondreference voltage applying circuit 61 is enabled for the n-th framescanning period. Thus, the reference voltage for the inverting amplifier22 held by the capacitor CAPV2 is applied to the positive input terminalof the inverting amplifier 22 connected to the vertical signal line 17B.

In addition, in this example, the row reset for the (n+1)th frame isperformed concurrently with the signal readout for the n-th frame duringthe 1H period. The row reset is performed using the vertical signal line17A. That is, among the odd numbered rows, the row reset for theselected row is performed. As illustrated in FIG. 15, during the 1Hperiod, the control signal to control the switch SWV_21 is set to “High”and, thus, the inverting amplifier 22 connected to the vertical signalline 17A is electrically connected to the first reference voltageapplying circuit 60 via the switch SWV_21. As illustrated in FIG. 10,the first reference voltage applying circuit 60 is enabled for the(n+1)th frame scanning period. Accordingly, the reference voltage forthe inverting amplifier 22 held by the capacitor CAPV1 is applied to thepositive input terminal of the inverting amplifiers 22 connected to thevertical signal line 17A.

During the next 1H in the overlapping period, the roles of the verticalsignal line 17A and the vertical signal line 17B are exchanged. That is,signal readout for the n-th frame and row reset for the (n+1)th frameare performed using the vertical signal line 17A and the vertical signalline 17B, respectively. When the vertical signal line 17A is discussed,the control signal to control the switch SWV_22 is set to “High” duringthe 1H period, as illustrated in FIG. 15. Accordingly, the secondreference voltage applying circuit 61 is electrically connected to theinverting amplifier 22 connected to the vertical signal line 17A. Atthat time, as can be seen from FIG. 10, the second reference voltageapplying circuit 61 is enabled and, thus, the reference voltage for theinverting amplifier 22 held by the capacitor CAPV2 is applied to thepositive input terminal of the inverting amplifier 22 connected to thevertical signal line 17A.

In contrast, the row reset for the (n+1)th frame is performed by usingthe vertical signal line 17B. When the vertical signal line 17B isdiscussed, the control signal to control the switch SWV_11 is set to“High” (refer to FIG. 15). Accordingly, the first reference voltageapplying circuit 60 is electrically connected to the inverting amplifier22 connected to the vertical signal line 17B. At that time, as can beseen from FIG. 10, the first reference voltage applying circuit 60 isenabled and, thus, the reference voltage for the inverting amplifier 22held by the capacitor CAPV1 is applied to the positive input terminal ofthe inverting amplifier 22 connected to the vertical signal line 17B.

In addition, in this example, during the overlapping period, each of theswitch SWV_SH_1 and the switch SWV_SH_2 in the sample-and-hold circuitis turned off. In this manner, each of the first reference voltageapplying circuit 60 and the second reference voltage applying circuit 61is enabled, and the reference voltage is supplied from each of the firstreference voltage applying circuit 60 and the second reference voltageapplying circuit 61 to the second switching circuit 62A.

According to the driving method described with reference to FIGS. 15 and10, feedback paths can be concurrently formed for the pixels 14 disposedin the odd numbered lines and in the pixels 14 disposed in the evennumbered lines in the same column. Thus, images can be captured at highframe rate.

Row Reset Period Hold and Signal Readout Period Hold

A driving method that differs from the driving method illustrated inFIGS. 10 and 15 is described below with reference to FIGS. 12 and 16.

FIG. 16 illustrates an example of the waveforms of the control signalsfor the switches SWV_11, SWV_12, SWV_21, and SWV_22 of the secondswitching circuit 62A. Signal waveforms illustrated in the middle ofFIG. 16 (“SWB_11”, “SWB_12”, “SWB_21”, and “SWB_22”) are described indetail below.

Even in the driving method, row reset is performed in a column by usingone of the vertical signal line 17A and the vertical signal line 17B. Atthe same time, signal readout is performed by using the other in thesame column. As can be seen from the lower section of FIG. 16, in thisexample, the first reference voltage applying circuit 60 is used forsignal readout in one of the even numbered rows and a given column. Inaddition, the second reference voltage applying circuit 61 is used forthe row reset serving as an electronic shutter in one of the oddnumbered rows in the column.

The leftmost 1H period in FIG. 16 is discussed below. During the 1Hperiod, signal readout is performed using the vertical signal line 17B,and the row reset is performed using the vertical signal line 17A. Atthat time, the control signal to control the switch SWV_11 is set to“High”, and the first reference voltage applying circuit 60 is enabled.In addition, the control signal to control the switch SWV_22 is set to“High”, and the second reference voltage applying circuit 61 is enabled.In contrast, during the next 1H period, signal readout is performedusing the vertical signal line 17A, and the row reset is performed usingthe vertical signal line 17B. At that time, the control signal tocontrol the switch SWV_21 is set to “High”, and the first referencevoltage applying circuit 60 is enabled. In addition, the control signalto control the switch SWV_12 is set to “High”, and the second referencevoltage applying circuit 61 is enabled. The timing of control of theswitches SWV_SH_1 and SWV_SH_2 performed by the first reference voltageapplying circuit 60 and the second reference voltage applying circuit 61can be the same as the timing of control in the second exemplaryembodiment described with reference to FIG. 12.

According to the driving method, in addition to the effect described inthe section “Row Reset Period Hold and Signal Readout Period Hold” forthe second exemplary embodiment, images can be captured at a high framerate, since feedback paths are concurrently formed in the pixels 14disposed in the odd numbered rows and the pixels 14 disposed in the evennumbered rows in the same column.

Fifth Exemplary Embodiment

A fifth exemplary embodiment of the present disclosure is describedbelow with reference to FIGS. 10, 12, 15, 16, and 17. Unlike the imagingdevice 1C according to the fourth exemplary embodiment, an imagingdevice 1D according to the present exemplary embodiment further includea bias circuit 40B including a third switching circuit 72A. Like thefourth exemplary embodiment, the present exemplary embodiment is appliedto a reference voltage applying circuit of a column feedbackconfiguration. The differences from the imaging device 1C according tothe fourth exemplary embodiment are mainly described below.

FIG. 17 is a schematic illustration of the circuit configuration of theimaging device 1D according to the fifth exemplary embodiment. Like theabove-described second switching circuit 62A, the third switchingcircuit 72A illustrated in FIG. 17 includes two pairs of switches. Inthis exemplary embodiment, a switch SWB_11 is connected between a loadunit 18 connected to the vertical signal line 17B and a signal line 73Athat is common to the columns of the pixels 14, and a switch SWB_12 isconnected between the load unit 18 and a signal line 73B that is commonto the columns of the pixels 14. In addition, a switch SWB_21 isconnected between the load unit 18 connected to the vertical signal line17A and the common signal line 73A, and a switch SWB_22 is connectedbetween the load unit 18 and a signal line 73B that is common to thecolumns of the pixels 14. The switch SWB_11 and the switch SWB_21 ineach of the columns are connected to the first bias circuit 70 via thecommon signal line 73A. The switch SWB_12 and a switch SWB_22 for eachof the columns are connected to the second bias circuit 71 via thecommon signal line 73B.

One Frame Scanning Period Hold

The signal waveforms of the control signals to control the switches inthe third switching circuit 72A are also illustrated in FIG. 15. Notethat the signal waveforms of the switches SWB_11, SWB_12, SWB_21, andSWB_22 are the same as the signal waveforms of the switches SWV_11,SWV_12, SWV_21, and SWV_22, respectively. That is, the switches of thethird switching circuit 72A and the switches of the second switchingcircuit 62A can be controlled at the same timing.

The time points at which the switches SWB_SH_1 and SWB_SH_2 provided inthe first bias circuit 70 and the second bias circuit 71, respectively,are controlled can be the same as those in the third exemplaryembodiment described with reference to FIG. 10.

According to the driving method, in addition to the effect described inthe section “One Frame Scanning Period Hold” for the third exemplaryembodiment, images can be captured at a high frame rate, since feedbackpaths are concurrently formed in the pixels 14 disposed in the oddnumbered rows and the pixels 14 disposed in the even numbered rows inthe same column.

Row Reset Period Hold and Signal Readout Period Hold

A driving method that differs from the driving method illustrated inFIGS. 10 and 15 is described below with reference to FIGS. 12 and 16.

FIG. 16 also illustrates an example of the waveforms of the controlsignals for the switches of the third switching circuit 72A. In thisexample, the signal waveforms of the switches SWB_11, SWB_12, SWB_21,and SWB_22 are the same as those of the switches SWV_11, SWV_12, SWV_21,and SWV_22, respectively. That is, the switches of the third switchingcircuit 72A and the switches of the second switching circuit 62A can becontrolled at the same timing.

The time points at which the switches SWB_SH_1 and SWB_SH_2 provided inthe first bias circuit 70 and the second bias circuit 71, respectively,are controlled can be the same as those in the third exemplaryembodiment described with reference to FIG. 12.

According to the driving method, in addition to the effect described inthe section “Row Reset Period Hold and Signal Readout Period Hold” forthe third exemplary embodiment, images can be captured at a high framerate, since feedback paths are concurrently formed in the pixels 14disposed in the odd numbered rows and the pixels 14 disposed in the evennumbered rows in the same column.

Sixth Exemplary Embodiment

In the above-described second to fifth exemplary embodiments, as anexample, the circuit configuration that allows a feedback path includingthe inverting amplifier 22 disposed so as to correspond to the verticalsignal line (the vertical signal line 17 or a pair consisting of thevertical signal lines 17A and 17B) to be formed is provided. However,the configuration of the feedback path is not limited thereto. Forexample, as described below, a circuit configuration in which a feedbackpath is closed in a pixel can be applied.

FIG. 18 illustrates an example of a circuit configuration of a pixelcapable of forming a feedback path. A pixel 14A illustrated in FIG. 18includes a photoelectric conversion unit 10 and a signal detectioncircuit SC that detects a signal generated by the photoelectricconversion unit 10. As illustrated in FIG. 18, the signal detectioncircuit SC includes an amplifier transistor 11 and an address transistor13. In the configuration illustrated in FIG. 18 as an example, thesignal detection circuit SC further includes a reset transistor 12, afeedback transistor 27, a first capacitative element 28, and a secondcapacitative element 29. One of a source and a drain of the resettransistor 12 is connected to a FD node that connects the photoelectricconversion unit 10 to a gate of the amplifier transistor 11. The otherof the source and the drain of the reset transistor 12 is connected to anode between the amplifier transistor 11 and the address transistor 13via a feedback line 26. The feedback transistor 27 and the firstcapacitative element 28 are connected between the source and the drainof the reset transistor 12. That is, the feedback transistor 27 and thefirst capacitative element 28 are connected between the FD node and thefeedback line 26. As illustrated in FIG. 18, one of two electrodes ofthe second capacitative element 29 is connected to a node between thefeedback transistor 27 and the first capacitative element 28(hereinafter, the node is also referred to as a “node RD”).

The gate of the reset transistor 12 is connected to a reset control line24 (not illustrated in FIG. 18, and refer to FIG. 3). When the imagingdevice operates, a reset control signal RST is applied to the gate ofthe reset transistor 12 via the reset control line 24. A verticalscanning circuit 15 (refer to FIG. 3) can reset the voltage of the FDnode of a selected pixel 14A by turning on the reset transistor 12 viathe reset control line 24. In this example, by turning on the resettransistor 12, the voltage of the feedback line 26 is applied to the FDnode.

The gate of the feedback transistor 27 is connected to a feedbackcontrol line (not illustrated). When the imaging device operates, afeedback control signal FB is applied to the gate of the feedbacktransistor 27 via the feedback control line. The feedback control lineis connected to, for example, the vertical scanning circuit 15. Thevertical scanning circuit can switch on/off the feedback transistor 27via the feedback control line.

As illustrated in FIG. 18, one of the source and the drain of thefeedback transistor 27 is electrically connected to the photoelectricconversion unit 10 via the first capacitative element 28. By setting anaddress control signal SEL for the gate of the address transistor 13 to,for example, a high level to turn on the address transistor 13 andfurther turning on the feedback transistor 27, a feedback path includingthe amplifier transistor 11 of the selected pixel 14A as part of thepath can be formed. The feedback path includes the feedback line 26connected between the source of the amplifier transistor 11 and thephotoelectric conversion unit 10 as part thereof. The feedback pathallows the output of the amplifier transistor 11 to be negatively fedback to one of the source and drain of the feedback transistor 27 whichis not connected to the node RD.

Typically, the second capacitative element 29 in the signal detectioncircuit SC has a capacitance value higher than the first capacitativeelement 28. When the imaging device operates, a reference voltage VR1(e.g., 0 V) is applied to the electrode of the second capacitativeelement 29 which is not connected to the node RD. The reference voltageVR1 may be a fixed voltage or, for example, a pulse voltage.

In the example illustrated in FIG. 18, constant current sources 91 and92 are connected to the vertical signal line 17 via a switching circuit90. When the imaging device operates, one end of the constant currentsource 91 and one end of the constant current source 92 are connected toa reference voltage (typically, ground (GND)) and a power source voltageVDD, respectively. Each of the constant current sources 91 and 92includes a load unit including, for example, a load transistor.

The switching circuit 90 includes a switch S1 connected between theconstant current source 91 and the vertical signal line 17 and a switchS2 connected between the constant current source 92 and the verticalsignal line 17. The switches S1 and S2 of the switching circuit 90 arecontrolled so as to be exclusively performed. That is, if the switch S1is turned on, the switch S2 is turned off. If the switch S1 is turnedoff, the switch S2 is turned on. As described below, according to thepresent exemplary embodiment, the switch S2 is turned on in resetting ofthe pixel 14A. In signal readout from the pixel 14A, the switch S1 isturned on.

A fourth switching circuit 82 is connected to the power source wiringline 21 connected to the drain of the amplifier transistor 11. In theexample illustrated in FIG. 18, the fourth switching circuit 82 includesa switch Ss1 and a pair consisting of switches SWI_1 and SWI_2. Theswitch Ss1 is connected between the power source wiring line 21 and avoltage line 87 to which a predetermined voltage VA (typically, VDD) isapplied when the imaging device operates. The switch SWI_1 is connectedbetween the power source wiring line 21 and a signal line 83A to which apredetermined voltage (typically, GND) is applied when the imagingdevice operates. The switch SWI_2 is connected between the power sourcewiring line 21 and a signal line 83B to which a predetermined voltage(typically, GND) is applied when the imaging device operates. The signallines 83A and 83B supply a predetermined drain voltage to the drain ofthe amplifier transistor 11. In a configuration in which a plurality ofpixels 14A are arranged two-dimensionally, each of the signal lines 83Aand 83B is a signal line common to all the columns of the pixels 14A.The magnitude of the voltage of the signal line 83A and the magnitude ofthe voltage of the signal line 83B are basically equivalent to eachother when the imaging device operates. That is, the magnitudes areequivalent to each other to the extent that the noise due to thedifference of these voltages cannot be recognized in the resultingimage. The switch Ss1 and the switches SWI_1 and SWI_2 are controlled sothat if the switch Ss1 is on, the switches SWI_1 and SWI_2 are turnedoff and, if the switch Ss1 is off, one of the switches SWI_1 and SWI_2is turned on.

In signal readout, the address transistor 13 is turned on, and theswitch S1 of the switching circuit 90 and the switch Ss1 of the fourthswitching circuit 82 are turned on. In this manner, an electric currentflows in a direction from the amplifier transistor 11 to the addresstransistor 13. At that time, the signal voltage in accordance with thecharge generated in the photoelectric conversion unit 10 is output tothe vertical signal line 17. That is, the voltage of the FD nodeamplified by the amplifier transistor 11 can be detected. That is, thesignal detection circuit SC can include an amplifier circuit as a partthereof.

In contrast, in resetting of the pixel 14A, the address transistor 13 isturned on, and the switch S2 of the switching circuit 90 and one of theswitch SWI_1 and the switch SWI_2 of the fourth switching circuit 82 areturned on. In this manner, an electric current flows in the amplifiertransistor 11 in a direction that is opposite from that in the signalreadout. At that time, by turning on the feedback transistor 27, afeedback path including the amplifier transistor 11, the feedback line26, the feedback transistor 27, and the first capacitative element 28 aspart thereof is formed. Accordingly, by forming the feedback path, kTCnoise can be prevented.

A typical example of the operations performed by the pixel 14A in signalreadout and in resetting is briefly described below. In signal readout,under the condition that the address transistor 13 is on, the switch Ss1of the fourth switching circuit 82 and the switch S1 of the switchingcircuit 90 are turned on. In this manner, the voltage VA is supplied tothe drain of the amplifier transistor 11 of the pixel 14A. The voltageVA can be the same as the power source voltage.

At that time, the amplifier transistor 11 and the constant currentsource 91 form a source follower, and a voltage in accordance with theamount of charge accumulated in the FD node is read out into thevertical signal line 17. The amplification factor of the source followeris about 1.

In contrast, in resetting of the pixel 14A, under the condition that theaddress transistor 13 is on, the reset transistor 12 and the feedbacktransistor 27 are turned on. At that time, one of the switches SWI_1 andSWI_2 of the fourth switching circuit 82 and the switch S2 of theswitching circuit 90 are turned on. By turning on the reset transistor12, the FD node is connected to the feedback line 26 via the resettransistor 12 and, thus, the pixel 14A is reset. That is, the signaldetection circuit SC includes a reset circuit including the resettransistor 12 and, in addition, the vertical scanning circuit 15connected to the reset control line 24 (refer to FIG. 3) serves as acircuit that supplies the control signal to control the reset circuit.

Thereafter, the reset transistor 12 is turned off. When the resettransistor 12 is turned off, kTC noise is generated. Accordingly, thekTC noise is added to the voltage of the FD node after resetting.However, since the feedback transistor 27 remains on, the condition thatforms the feedback path that negatively feeds back the output of theamplifier transistor 11 to one of the source and the drain of thefeedback transistor 27 still continues. Accordingly, the kTC noisegenerated by turning off the reset transistor 12 is reduced to1/(1+A)^(1/2), where A represents the gain of the feedback.

Subsequently, the voltage level of the feedback control signal FB isdecreased to, for example, a level between the high level and the lowlevel. Thereafter, the feedback control signal FB is set to the lowlevel. By setting the voltage level of the feedback control signal FB toa level lower than the high level, the operating bandwidth of thefeedback transistor 27 is decreased from that when the feedback controlsignal FB is at the high level. If the feedback control signal FBreaches the low level, the feedback transistor 27 is turned off, and theformed feedback path disappears. At that time, if the operatingbandwidth of the feedback transistor 27 is lower than the operatingbandwidth of the amplifier transistor 11, the kTC noise generated byturning off the feedback transistor 27 is reduced from that generatedwhen no feedback path is formed. If the amplification factor of anamplifier formed by the fourth switching circuit 82 and the amplifiertransistor 11 is set to (−D), the kTC noise generated by turning off thefeedback transistor 27 is reduced to (1/(1+D))^(1/2) times the kTC noisegenerated when no feedback path is generated. In this manner, by usingthe feedback control signal FB, band limiting by the feedback transistor27 can be performed. Note that the value of D is greater than 1 and canbe set to a value in the range from several tens to several hundreds.

In this example, by switching the electric current to the pixel 14A, theamplifier transistor 11 is allowed to function as a source follower insignal readout, and the amplifier transistor 11 is allowed to functionas a common source in resetting of the pixel 14A. In this manner, evenwhen the feedback path is formed in each of the pixels 14A, the kTCnoise remaining in the FD node can be reduced from that generated whenno feedback is provided. The following control may be performed. Thatis, a slope voltage may be used as the feedback control signal FB, andthe voltage level of the feedback control signal FB may be decreasedfrom the high level to the low level.

In the example of configuration illustrated in FIG. 18, the signaldetection circuit SC includes a capacitance circuit including seriesconnection of the first capacitative element 28 and the secondcapacitative element 29 between the FD node and the reference voltageVR1. Accordingly, let B be the attenuation rate obtained by thecapacitance circuit. Then, the magnitude of the kTC noise added to thevoltage of the FD node when the feedback transistor 27 is turned off canbe reduced to (1+(1+A·B)·Cfd/C2)^(1/2)/(1+A·B) times the magnitude ofthe kTC noise generated when the feedback transistor 27 is directlyconnected to the FD node without providing a capacitance circuit in thesignal detection circuit SC. In this manner, by providing the firstcapacitative element 28 and the second capacitative element 29 in thesignal detection circuit SC, the magnitude of the kTC noise added to thevoltage of the FD node can be reduced more. Note that Cfd and C2 in theabove expression represent the capacitance value of the FD node and thecapacitance value of the second capacitative element 29, respectively.

The above-described technique for reducing the kTC noise can be appliedto even the circuit configuration of a pixel 14B illustrated in FIG. 19.In the configuration illustrated in FIG. 19 as an example, the resettransistor 12 is connected to the first capacitative element 28 inparallel. That is, in the example illustrated in FIG. 19, one of thesource and the drain of the reset transistor 12 that is not connected tothe FD node is connected to an RD node. Even such a configuration canreduce the magnitude of the kTC noise added to the voltage of the FDnode by applying the above-described operation. Note that in the exampleof configuration illustrated in FIG. 18, one of the source and the drainof the reset transistor 12 that is not connected to the FD node isdirectly connected to the feedback line 26. Accordingly, the flexibilityof the design of an impurity profile for ensuring the driving power ofthe reset transistor 12 can be advantageously increased.

The imaging device according to the sixth exemplary embodiment of thepresent disclosure is described below with reference to FIGS. 20A and20B, FIG. 8A, and FIGS. 10, 12, 14, 15, 16, and 17.

FIG. 20A is a schematic illustration of the circuit configuration of animaging device 1E according to the sixth exemplary embodiment. Theimaging device 1E illustrated in FIG. 20A includes a plurality of pixels14A arranged two-dimensionally. In this example, for simplicity of thedrawings, only five of the pixels 14A in a given column of the pixels14A are illustrated. Note that instead of the pixels 14A, the pixels 14Bdescribed above with reference to FIG. 19 can be applied.

Like the imaging device 10 illustrated in FIG. 14 and the imaging device1D illustrated in FIG. 17, the imaging device 1E in the example ofconfiguration illustrated in FIG. 20A includes two vertical signallines, that is, a vertical signal line 17A and a vertical signal line17B for each of the columns of the pixels 14A. The source of theamplifier transistor 11 of each of the pixels 14A in the odd numberedrows is electrically connected to the vertical signal line 17A, and thesource of the amplifier transistor 11 of each of the pixels 14A in theeven numbered rows is electrically connected to the vertical signal line17B. Note that two vertical signal lines, that is, the vertical signallines 17A and 17B need not be always provided for each of the columns ofthe pixels 14A. For example, like the example illustrated in FIG. 8A, aconfiguration in which only one vertical signal line may be provided foreach of the columns of the pixels 14A may be employed.

As illustrated in FIG. 20A, as the vertical signal lines 17A and 17B aredisposed for each of the columns of the pixel 14A, a switching circuit90 o is connected between the vertical signal line 17A and a constantcurrent source, and a switching circuit 90 e is connected between thevertical signal line 17B and the constant current source. The switchingcircuit 90 o includes switches So1 and So2. The switching circuit 90 eincludes switches Se1 and Se2. The switches So1 and So2 correspond tothe switches S1 and S2 illustrated in FIG. 18, respectively, and can becontrolled in the same manner as the switches S1 and S2. In addition,the switches Se1 and Se2 correspond to the switches S1 and S2illustrated in FIG. 18, respectively, and can be controlled in the samemanner as the switches S1 and S2.

In this example, two vertical signal lines, that is, the vertical signallines 17A and 17B are disposed for each of the columns of the pixels14A, two power source wiring lines, that is, the power source wiringlines 21A and 21B are disposed for each of the columns of the pixels14A. As illustrated in FIG. 20A, the power source wiring lines 21A and21B for each of the columns are connected to the pixels 14A disposed inthe odd numbered rows and the pixels 14A disposed in the even numberedrows, respectively.

In the example of configuration illustrated in FIG. 20A, the imagingdevice 1E includes a drain voltage applying circuit 80A which includes afourth switching circuit 82A, a first drain voltage applying circuit 80,and a second drain voltage applying circuit 81. In this example, as thepower source wiring lines 21A and 21B are disposed for each of thecolumns of the pixel 14A, the fourth switching circuit 82A is connectedbetween each of the power source wiring lines 21A and 21B and each ofsignal lines 83A and 83B and between each of the power source wiringlines 21A and 21B and the voltage line 87.

The fourth switching circuit 82A includes switches Sso1, SWI_21, andSWI_22 each having one end connected to the power source wiring line 21Aand switches Sse1, SWI_11, and SWI_12 each having one end connected tothe power source wiring line 21B. As illustrated in FIG. 20A, the otherend of each of the switches Sso1 and Sse1 is connected to the voltageline 87. The other end of each of the switches SWI_21 and SWI_11 isconnected to the signal line 83A. The other end of each of the switchesSWI_22 and SWI_12 is connected to the signal line 83B.

The switches Sso1, SWI_21, and SWI_22 correspond to the switches Ss1,SWI_1, and SWI_2 illustrated in FIG. 18 and are controlled in the samemanner as the switches Ss1, SWI_1, and SWI_2, respectively. Similarly,the switches Sse1, SWI_11, and SWI_12 correspond to the switches Ss1,SWI_1, and SWI_2 illustrated in FIG. 18 and are controlled in the samemanner as the switches Ss1, SWI_1, and SWI_2, respectively. Accordingly,for example, if the switch Sso1 is on, the switches SWI_21 and SWI_22are off.

The signal lines 83A and 83B are connected to the drain voltage applyingcircuit 80A. In this example, the signal lines 83A and 83B are connectedto the first drain voltage applying circuit 80 and the second drainvoltage applying circuit 81, respectively. That is, in this example, thefirst drain voltage applying circuit 80 and the second drain voltageapplying circuit 81 can be electrically connected to the drain of theamplifier transistor 11 of the pixel 14A via the fourth switchingcircuit 82A. Each of the first drain voltage applying circuit 80 and thesecond drain voltage applying circuit 81 generates the drain voltage ofthe amplifier transistor 11 of the pixel 14A. The magnitudes of thedrain voltages generated by the first drain voltage applying circuit 80and the second drain voltage applying circuit 81 are equivalent to eachother. In other word, the magnitudes are equivalent to each other to theextent that the noise due to the difference of these drain voltagescannot be recognized in the resulting image.

Each of the first drain voltage applying circuit 80 and the second drainvoltage applying circuit 81 can include a sample-and-hold circuit. Inthe example illustrated in FIG. 20A, the first drain voltage applyingcircuit 80 includes an output buffer 85A, a capacitor CAPI1, a switchSWI_SH_1, and a voltage control unit 84A. Similarly, the second drainvoltage applying circuit 81 includes an output buffer 85B, a capacitorCAPI2, a switch SWI_SH_2, and a voltage control unit 84B. The capacitorsCAPI1 and CAPI2 and the voltage control units 84A and 84B may bedisposed outside the imaging device 1E.

For example, if the switch SWI_SH_1 is turned on, the output voltagefrom the voltage control unit 84A is charged in the capacitor CAPI1(sampling). If the switch SWI_SH_1 is turned off, the sample operationis completed, and the sampled voltage signal is held in the capacitorCAPI1 (hold). In the same manner, a sample operation and a holdoperation are performed in the second drain voltage applying circuit 81.The voltage signals held in the capacitors CAPI1 and CAPI2 are output tothe fourth switching circuit 82A via the output buffers 85A and 85B,respectively. The fourth switching circuit 82A can be controlled by, forexample, a peripheral logic circuit (not illustrated).

If the switch SWI_21 and the switch So2 are turned on, the first drainvoltage applying circuit 80 is electrically connected to the powersource wiring line 21A. Accordingly, a predetermined drain voltage(typically, GND) sampled into the capacitor CAPI1 can be applied to thedrain of the amplifier transistor 11 of the pixel 14A in the selectedrow (one of the odd numbered rows). In addition, if the switch Sso1 andthe switch So1 are turned on, the output of the pixel 14A in theselected row (one of the odd numbered rows) can be read out into thevertical signal line 17A. Similarly, if the switch SWI_22 and the switchSo2 are turned on, the second drain voltage applying circuit 81 iselectrically connected to the power source wiring line 21A. Accordingly,a predetermined drain voltage (typically, GND) sampled into thecapacitor CAPI2 can be applied to the drain of the amplifier transistor11 of the pixel 14A of the selected row (one of the odd numbered rows).By controlling the switches Sse1, SWI_11, and SWI_12 and controlling theswitches Set and Se2, a similar operation can be performed on the pixel14A of an even numbered row.

In this example, the switch Sso1 and the pair consisting of the switchesSWI_21 and SWI_22, and the switch Sse1 and the pair consisting ofswitches SWI_11 and SWI_12 are provided for each of the each of thecolumns of the pixels 14A. Accordingly, resetting of one of two pixels14A disposed in the same column and signal readout from the other pixel14A can be performed at the same time.

One Frame Scanning Period Hold

Even in the sixth exemplary embodiment, the imaging device can operatein a manner that is almost the same as the imaging devices according tothe fourth and fifth exemplary embodiments. For example, the imagingdevice can perform an operation that is the same as illustrated in FIGS.15 and 10.

For example, in the same column, the second drain voltage applyingcircuit 81 may be connected to the vertical signal line 17B (or thevertical signal line 17A) in the row reset period and the signal readoutperiod according to the n-th frame, and the first drain voltage applyingcircuit 80 may be connected to the vertical signal line 17A (or thevertical signal line 17B) in the row reset period and the signal readoutperiod according to the (n+1)th frame. That is, the fourth switchingcircuit 82A may be controlled so that the second drain voltage applyingcircuit 81 is electrically connected to the drain of the amplifiertransistor 11 of one of the pixels 14A in an even numbered row for then-th frame, and the first drain voltage applying circuit 80 iselectrically connected to the drain of the amplifier transistor 11 ofone of the pixels 14A in an odd numbered row for the (n+1)th frame.

In such a case, for resetting of the pixel 14A, on/off of the switchSWI_12 and the switch Se2 can be made to correspond to on/off of theswitch SWV_12 illustrated in FIG. 15. That is, the switch SWI_12 and theswitch Se2 can be turned on and off in the same manner as the switchSWV_12 is turned on and off, as illustrated in FIG. 15. In addition,on/off of the switch SWI_22 and the switch So2 can be made to correspondto on/off of the switch SWV_22 illustrated in FIG. 15. Similarly, on/offof the switch SWI_11 and the switch Se2 can be made to correspond toon/off of the switch SWV_11 illustrated in FIG. 15. On/off of the switchSWI_21 and the switch So2 can be made to correspond to on/off of theswitch SWV_21 illustrated in FIG. 15. The switches SWI_SH_1 and SWI_SH_2can be turned on and off in the same manner as the switches SWV_SH_1 andSWV_SH_2 are turned on and off, as illustrated in FIG. 10. Note that forsignal readout from the pixel 14A, for example, signal readout for thepixel 14A in an even numbered row, on and off of the switch SWV_12 canbe replaced with on and off of the switch Sse1 and the switch Se1 asillustrated in FIG. 15. For signal readout from the pixel 14A in an oddnumbered row, on and off of the switch SWV_22 can be replaced with onand off of the switch Sso1 and the switch So1 as illustrated in FIG. 15.

According to the driving method, in addition to the effect described inthe section “One Frame Scanning Period Hold” for the third exemplaryembodiment, images can be captured at a high frame rate, since feedbackpaths are concurrently formed for the pixels 14A disposed in the oddnumbered rows and the pixels 14A disposed in the even numbered rows inthe same column.

Row Reset Period Hold and Signal Readout Period Hold

Even in the sixth exemplary embodiment, an operation that is the same asthe operation illustrated in FIGS. 12 and 16 can be applied. That is,the fourth switching circuit 82A may be controlled so that during therow reset period in one frame period, the second drain voltage applyingcircuit 81 is electrically connected to the drain of the amplifiertransistor 11 in one of the pixels 14A in an odd numbered row (or aneven numbered row) and during the pixel signal readout period in the oneframe period, the first drain voltage applying circuit 80 iselectrically connected to the drain of the amplifier transistor 11 ofone of the pixels 14A in an even numbered row (or an odd numbered row).

In such a case, as described in the example of the operation in thesection “One Frame Scanning Period Hold”, for resetting of the pixel14A, on and off of the switch SWI_12 and the switch Se2 can be made tocorrespond to on and off of the switch SWV_12 as illustrated in FIG. 16.On and off of the switch SWI_22 and the switch So2 can be made tocorrespond to on and off of the switch SWV_22 illustrated in FIG. 16.Similarly, on and off of the switch SWI_11 and the switch Se2 can bemade to correspond to on and off of the switch SWV_11 illustrated inFIG. 16. On and off of the switch SWI_21 and the switch So2 can be madeto correspond to on/off of the switch SWV_21 illustrated in FIG. 16. Theswitches SWI_SH_1 and SWI_SH_2 can be turned on and off in the samemanner as the switches SWVSH_1 and SWV_SH2 are turned on and off, asillustrated in FIG. 12.

According to the driving method, the hold operation performed by thesample-and-hold circuit of one of the first drain voltage applyingcircuit 80 and the second drain voltage applying circuit 81 can bemaintained throughout the row reset period and throughout the signalreadout period. According to the driving method, in addition to theeffect described in the section “Row Reset Period Hold and SignalReadout Period Hold” for the third exemplary embodiment, images can becaptured at a high frame rate, since feedback paths can be concurrentlyformed in the pixel 14A disposed in an odd numbered row and the pixel14A disposed in an even numbered row in the same column.

As illustrated in FIG. 20B, a drain voltage applying circuit 80B inwhich instead of the drain voltage applying circuit 80A, a first drainvoltage applying circuit 80D and a second drain voltage applying circuit81D are provided and a voltage control unit 84D is shared by the firstdrain voltage applying circuit 80D and the second drain voltage applyingcircuit 81D may be employed. By sharing the voltage control unit, thesize of the drive circuit unit can be advantageously reduced. Thevoltage control unit 84D may be disposed either inside or outside theimaging device 1E. Note that instead of disposing the switches Sso1,SWI_21, and SWI_22 and the switches Sse1, SWI_11, and SWI_12 for each ofthe columns of the pixels 14A, a set of the switches Sso1, SWI_21, andSWI_22 may be connected between the signal line 83A and the first drainvoltage applying circuit 80, and a set of Sse1, SWI_11, and SWI_12 maybe connected between the signal line 83B and the second drain voltageapplying circuit 81.

FIG. 21 illustrates a modification of the circuit configurationaccording to the sixth exemplary embodiment. In FIG. 21, for simplicityof the drawings, only one of the plurality of pixels 14A is illustrated.

As illustrated in FIG. 21, the configuration illustrated in FIG. 13A maybe applied to the constant current source 92 used to reset the pixel14A. In the configuration illustrated in FIG. 21 as an example, the biascircuit 40A illustrated in FIG. 13A is connected to the switch S2 of theswitching circuit 90. Like the third exemplary embodiment, by performingswitch control on the third switching circuit 72, a variation of thebias voltage in resetting of the pixel 14A can be prevented and, thus,random horizontal line noise can be effectively prevented. Note thatinstead of the bias circuit 40A, the bias circuit 40D illustrated inFIG. 13B may be employed.

According to the sixth exemplary embodiment, the variation of the drainvoltage of an amplifier transistor caused by disturbance noise orthermal noise can be prevented. In addition, according to the sixthexemplary embodiment, since the amplifier transistor 11 of each of thepixels functions as a signal detection circuit transistor of the signaldetection circuit SC and an amplifier transistor of the feedbackcircuit, the need for an inverting amplifier for each of the columns ofthe pixels can be eliminated. Accordingly, the size and the powerconsumption of the imaging device can be advantageously reduced.

The imaging device of the present disclosure is applicable to a varietyof camera systems and sensor systems, such as digital still cameras,cameras for medical use, security cameras, in-vehicle cameras, digitalsingle-lens reflex cameras, and digital mirrorless single-lens reflexcameras.

What is claimed is:
 1. An imaging device comprising: a pixel comprising:a photoelectric converter that converts incident light into charges, anda reset transistor having a first source, a first drain and a firstgate, one of the first source and the first drain coupled to thephotoelectric converter; first voltage generating circuity thatgenerates a first voltage; second voltage generating circuity thatgenerates a second voltage, the second voltage generating circuity beingdifferent from the first voltage generating circuity; and firstswitching circuity that causes either the first voltage generatingcircuity or the second voltage generating circuity to selectively coupleto the other of the first source and the first drain of the resettransistor.
 2. The imaging device according to claim 1, wherein thefirst voltage generating circuity includes a first capacitor for holdingthe first voltage, and the second voltage generating circuity includes asecond capacitor for holding the second voltage, the second capacitorbeing different from the first capacitor.
 3. The imaging deviceaccording to claim 1, wherein the first voltage is equivalent to thesecond voltage.
 4. The imaging device according to claim 1, furthercomprising: an inverting amplifier having a first input terminal, asecond input terminal and an output terminal, the output terminal beingcoupled to the other of the first source and the first drain of thereset transistor, wherein the pixel includes an amplifier transistorhaving a second source, a second drain and a second gate, the secondgate being coupled to the photoelectric converter, one of the secondsource and the second drain being coupled to the first input terminal ofthe inverting amplifier, and the first switching circuity causes eitherthe first voltage generating circuity or the second voltage generatingcircuity to selectively couple to the second input terminal of theinverting amplifier, to thereby cause either the first voltagegenerating circuity or the second voltage generating circuity toselectively couple to the other of the first source and the first drainof the reset transistor.
 5. The imaging device according to claim 3,further comprising: load circuity coupled to the one of the secondsource and the second drain of the amplifier transistor; third voltagegenerating circuity that generates a third voltage; fourth voltagegenerating circuity that generates a fourth voltage; and secondswitching circuity that causes either the third voltage generatingcircuity or the fourth voltage generating circuity to selectively coupleto the load circuity.
 6. The imaging device according to claim 1,wherein the pixel includes an amplifier transistor having a secondsource, a second drain and a second gate, the second gate being coupledto the photoelectric converter, one of the second source and the seconddrain being coupled to the other of the first source and the first drainof the reset transistor, and the first switching circuity causes eitherthe first voltage generating circuity or the second voltage generatingcircuity to selectively couple to the other of the second source and thesecond drain of the amplifier transistor, to thereby cause either thefirst voltage generating circuity or the second voltage generatingcircuity to selectively couple to the other of the first source and thefirst drain of the reset transistor.
 7. The imaging device according toclaim 6, wherein the pixel includes an feedback transistor having athird source, a third drain and a third gate, one of the third sourceand the third drain being coupled to the other of the first source andthe first drain of the reset transistor, the other of the third sourceand the third drain being coupled to the one of the second source andthe second drain of the amplifier transistor.
 8. The imaging deviceaccording to claim 6, further comprising: load circuity coupled to theother of the second source and the second drain of the amplifiertransistor; third voltage generating circuity that generate a thirdvoltage; fourth voltage generating circuity that generates a fourthvoltage; and second switching circuity that causes either the thirdvoltage generating circuity or the fourth voltage generating circuity toselectively couple to the load circuity.
 9. The imaging device accordingto claim 1, wherein the first switching circuity causes the firstvoltage generating circuity to couple to the other of the first sourceand the first drain of the reset transistor in a first period includedin a first frame period according to a first frame, and the firstswitching circuity causes the second voltage generating circuity tocouple to the other of the first source and the first drain of the resettransistor in a second period included in a second frame periodaccording to a second frame subsequent to the first frame.
 10. Theimaging device according to claim 1, wherein the first switchingcircuity causes the first voltage generating circuity to couple to theother of the first source and the first drain of the reset transistor ina first period included in a first frame period according to a firstframe, and the first switching circuity causes the second voltagegenerating circuity to couple to the other of the first source and thefirst drain of the reset transistor in a second period included in thefirst frame period, the second period being different from the firstperiod.
 11. The imaging device according to claim 1, wherein each of thefirst voltage generating circuity and the second voltage generatingcircuity includes a sample hold circuity.
 12. The imaging deviceaccording to claim 5, wherein each of the third voltage generatingcircuity and the fourth voltage generating circuity includes a samplehold circuity.
 13. The imaging device according to claim 8, wherein eachof the third voltage generating circuity and the fourth voltagegenerating circuity includes a sample hold circuity.